Electrophotographic photoreceptor, method for manufacturing the electrophotographic photoreceptor, and image forming method, image forming apparatus and process cartridge using the electrophotographic photoreceptor

ABSTRACT

A photoreceptor including a photosensitive layer including a specific diamine compound, or a photoreceptor including an electroconductive substrate; a photosensitive layer located overlying the electroconductive substrate; and optionally a protective layer located overlying the photosensitive layer, wherein an outermost layer of the photoreceptor includes a filler, an organic compound having an acid value of from 10 to 700 mgKOH/g and a specific diamine compound. An image forming method, an image forming apparatus and a process cartridge using the photoreceptor are also provided. A method for manufacturing the photoreceptor including the steps of preparing a coating liquid including the filler, the organic compound, the specific diamine compound and an antioxidant; and coating the coating liquid is also provided.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an electrophotographicphotoreceptor. In addition, the present invention also relates to amethod for manufacturing the electrophotographic photoreceptor, and anelectrophotographic image forming method and apparatus and a processcartridge using the electrophotographic photoreceptor.

[0003] 2. Discussion of the Background

[0004] Recently, development of the information processing systems usingelectrophotography is remarkable. In particular, improvement in theprint qualities and reliability of laser printers and digital copiers,in which image information is recorded using light after information isconverted to digital signals, is remarkable. In addition, the techniqueis applied to full color laser printers and full color digital copierswhile being combined with a high speed recording technique. Therefore, aneed exists for a photoreceptor which can produce high quality imageswhile having a good durability.

[0005] As the electrophotographic photoreceptor (hereinafter referred toas a photoreceptor) for use in electrophotographic image formingapparatus, inorganic photoreceptors using a material such as selenium oramorphous silicon and organic photoreceptors are known. Among thesephotoreceptors, organic photoreceptors have been typically used nowbecause of having low costs and good productivity and beingnon-polluting.

[0006] Specific examples of the organic photoreceptors includephotoreceptors having the following photosensitive layers:

[0007] (1) photosensitive layers including a photoconductive resintypified by polyvinylcarbazole (PVK);

[0008] (2) photosensitive layers including a charge transfer complextypified by polyvinylcarbazole-2,4,7-trinitrofluorenon (PVK-TNF);

[0009] (3) photosensitive layers including a pigment dispersion typifiedby a phthalocyanine-binder system; and

[0010] (4) functionally-separated photosensitive layers using acombination of a charge generation material and a charge transportmaterial.

[0011] Among these organic photoreceptors, the functionally-separatedphotoreceptors are widely used now because of having highphotosensitivity, good durability and good flexibility in selectingappropriate charge generation materials and charge transport materials.

[0012] The mechanism of forming an electrostatic latent image on afunctionally-separated photoreceptor is as follows:

[0013] (1) when imagewise light irradiates a charged photoreceptor, theimagewise light is absorbed by a charge generation material in a chargegeneration layer after passing through a transparent charge transportlayer located overlying the charge generation layer;

[0014] (2) the charge generation material absorbing light generates acharge carrier;

[0015] (3) the charge carrier is injected into the charge transportlayer and transported through the charge transport layer (or thephotosensitive layer) due to an electric field generated by the chargeformed on the surface of the photoreceptor; and

[0016] (4) the charge carrier neutralizes the charge on the surface ofthe photoreceptor, resulting in formation of an electrostatic latentimage.

[0017] However, organic photoreceptors have drawbacks in that thephotosensitive layers thereof are greatly abraded after repeated use,thereby deteriorating the potential formed on the photoreceptors andphotosensitivity thereof, and in addition the resultant images havebackground development caused by scratches on the surface of thephotoreceptor and low image density. Therefore, it has been attempted toimprove the abrasion resistance of photoreceptors. In addition, recentlyelectrophotographic image forming apparatus are required to be small insize and to perform high speed image formation. Therefore, thephotoreceptors for use in such image forming apparatus need to have gooddurability.

[0018] In attempting to improve the durability of photoreceptors, thefollowing methods have been proposed:

[0019] (1) a protective layer having good lubricity is formed as anoutermost layer;

[0020] (2) a crosslinked protective layer is formed as the outermostlayer; and

[0021] (3) a protective layer including a filler is formed as outermostlayer.

[0022] Among these methods, the third method is effective at improvingthe durability of the photoreceptors. However, when a filler having ahigh insulation property is included in the protective layer, theresistance of the photoreceptor increases, and thereby a problem ofserious increase in residual potential (hereinafter referred to as aresidual potential increasing problem) is caused. This problem isconsidered to be caused by increase in resistance thereof and number ofcharge trap sites therein. In contrast, when an electroconductive filleris used in the protective layer, the resistance of the photoreceptordecreases, and therefore the problem of serious increase in residualpotential is not caused. However, other problems such that outlines ofthe resultant images blur (hereinafter referred to as a blurred imageproblem), and thereby image qualities deteriorate.

[0023] Therefore, a technique in that a filler having a relatively lowinsulation property is used for the protective layer while thephotoreceptor is heated by a heater such as drum heaters to preventoccurrence of the blurred image problem. In this case, the blurred imageproblem can be avoided, but the diameter of the photoreceptor has to beincreased. Therefore, this technique cannot be applied to photoreceptorshaving a small diameter and small-sized image forming apparatus); Inaddition, by using a drum heater, the resultant image forming apparatushave the following drawbacks:

[0024] (1) the electric power consumption of the image forming apparatusincreases; and

[0025] (2) the waiting time (i.e., the time needed for activating theimage forming apparatus from switching on) is long.

[0026] In contrast, when a filler having a high insulation property isused, the residual potential increasing problem occurs. In this case,the potential of lighted portions of the photoreceptor increases, andthereby the image density and half-tone property of the resultant imagesdeteriorate. In attempting to solve this problem, a technique in thatthe potential of non-lighted portions of the photoreceptor is increasedis proposed. However, in this case, other problems such that backgrounddevelopment is caused due to increase in electric field formed on thephotoreceptor, and the life of the photoreceptor is shortened occur.

[0027] In addition, in attempting to solve the residual potentialincreasing problem, published examined Japanese Patent Applications Nos.44-834, 43-16198 and 49-10258 have disclosed techniques in that aprotective layer having a photoconductivity is formed as an outermostlayer. However, the photoreceptors have a drawback in that the quantityof the imagewise light reaching the photosensitive layer located belowthe protective layer decreases because the protective layer absorbs theirradiated light, resulting in deterioration of the photosensitivity ofthe photoreceptor.

[0028] In attempting to improve the abrasion resistance, publishedunexamined Japanese Patent Application No. (hereinafter referred to asJOP) 57-30846 discloses a photoreceptor in which a protective layerincluding a filler such as a metal or a metal oxide, which has aparticle diameter not greater than 0.3 μm, is formed as an outermostlayer of the photoreceptor, to increase the transparency of theprotective layer (i.e., to prevent increase of residual potential). Byusing this method, the increase of residual potential can be preventedto some extent. However, the effect is insufficient, and the residualpotential increasing problem cannot be fully solved. This is because theproblem is mainly caused by charge trapping by the added filler, whichdepends on the dispersion conditions of the filler in the protectivelayer. Even when the particle diameter of the filler is greater than 0.3μm, the transparency of the resultant protective layer can be increasedif the filler has good dispersibility. In contrast, even when theparticle diameter is not greater than 0.3 μm, the transparency of theresultant protective layer is low if the filler has poor dispersibility.

[0029] Further, JOP 4-281461 discloses a photoreceptor, in which acharge transport material is included in a protective layer togetherwith a filler to prevent increase of residual potential whilemaintaining good abrasion resistance. By including a charge transportmaterial in the protective layer, the mobility of charges in theprotective layer can be improved and thereby the increase of residualpotential can be prevented to some extent. However, as mentioned above,the problem is mainly caused by increase in number of charge trappingsites, and therefore, there is a limitation on the residual potentialimproving effect by this method. Therefore, in this case, the thicknessof the protective layer and the content of filler in the protectivelayer have to be decreased, and thereby good durability cannot beimparted to the resultant photoreceptor.

[0030] Further, in attempting to solve the residual potential increasingproblem, JOP 53-133444 discloses a photoreceptor in which a Louis acidis included in the protective layer; JOP 55-157748 discloses aphotoreceptor in which an organic proton acid is included in aprotective layer together with a filler; JOP 2-4275 discloses aphotoreceptor in which an electron accepting material is included in aprotective layer; and JOP 2000-66434 discloses a photoreceptor in whicha wax having an acid value not greater than 5 mgKOH/g is included in theprotective layer.

[0031] By using these methods, the injection property of charges at theinterface between the protective layer and the charge transport layercan be improved, because portions having a relatively low resistance areformed in the protective layer and thereby the charges can easily reachthe surface of the protective layer. However, these photoreceptors havea drawback in that the blurred image problem is caused. In addition,when an organic acid is included in the protective layer, dispersibilityof the filler deteriorates, and thereby good residual potentialimproving effect cannot be produced.

[0032] In order to produce high quality images using a photoreceptorhaving a filler-containing protective layer, not only occurrence of theresidual potential increasing problem and the blurred image problem hasto be prevented, but also the photoreceptor has to have a property suchthat charges generated in the photoreceptor can linearly reach thesurface of the photoreceptor without being obstructed by the filler inthe protective layer.

[0033] Whether or not charges can linearly advance through theprotective layer depends on the dispersibility of the filler in theprotective layer. Specifically, when the filler in the protective layeris aggregated, advancement of the charges, which are injected into theprotective layer from the charge transport layer, to the surface of theprotective layer is obstructed by the filler in the protective layer. Asa result, toner particles are scattered in the resultant toner image,resulting in serious deterioration of the resolution of the toner image.

[0034] In addition, in a case where image writing light is scattered atthe filler included in the protective layer and thereby the lighttransmission is deteriorated, the resolution of the resultant tonerimages is also deteriorated. The scattering of image writing light alsochanges depending on the dispersion conditions of the filler in theprotective layer.

[0035] Further, the dispersion conditions of the filler in theprotective layer greatly influence on the abrasion resistance of theprotective layer. Specifically, a filler is unevenly dispersed in theprotective layer, the abrasion resistance of the protective layerdeteriorates.

[0036] Therefore, in the photoreceptor having a protective layer inwhich a filler is dispersed to improve the durability of thephotoreceptor, it is important to improve the dispersibility of thefiller therein.

[0037] However, there is no photoreceptor which includes afiller-containing protective layer and which can produce high qualityimages without causing the blurred image problem and the residualpotential increasing problem while having good durability. As mentionedabove, when a drum heater is used for preventing occurrence of theblurred image problem, other problems in that the image formingapparatus becomes large in size, and the power consumption thereofincreases are caused.

[0038] JOP 2000-231204 discloses an aromatic compound havingdialkylamino group which serves as an acid scavenger. It is describedtherein that this compound is effective at improving image qualitiesafter repeated use, namely effective at solving the blurred imageproblem caused by oxidizing materials. However, the compound has poorcharge transport ability, and therefore the compound cannot be used forphotoreceptors for use in high speed image forming apparatus. Therefore,the compound cannot be included in a photoreceptor in a small quantity,and thereby the effect is little.

[0039] Further, JOP 60-196768 and Japanese Patent No. 2884353 (i.e., JOP03-96961) have disclosed stilbene compounds having a dialkylamino group.It is reported by Itami et al. in Konica technical Report, Vol. 13, P37, 2000 that the compounds are effective at improving the blurred imageproblem. However, the dialkylamino group of the stilbene compounds has astrong mesomeric effect (i.e., +M effect) against the triaryl aminestructure which is a charge transport site. Therefore, the ionizationpotential of the entire system seriously decreases. Therefore the chargeretaining ability of the charge transport material therein deterioratesat the beginning or after repeated use. Therefore the photoreceptor isnot practically used. Even if the stilbene compounds are used togetherwith other charge transport materials, the resultant photoreceptors havevery low photosensitivity and high residual potential. This is becausethe ionization potential of the stilbene compounds is very low relativeto that of the charge transport materials and therefore the stilbenecompounds serve as trap sites.

[0040] Because of these reasons, a need exists for a photoreceptor whichhas good durability and which can produce high quality images withoutcausing the blurred image problem and the residual potential increasingproblem.

SUMMARY OF THE INVENTION

[0041] Accordingly, an object of the present invention is to provide aphotoreceptor which has good durability and which can produce highquality images without causing the blurred image problem and theresidual potential increasing problem, and a method for manufacturingthe photoreceptor.

[0042] Another object of the present invention is to provide an imageforming method by which high quality images can be produced at a highspeed for a long period of time without frequently changing thephotoreceptor.

[0043] Yet another object of the present invention is to provide animage forming apparatus and a process cartridge, which is small in sizeand which can produce high quality images at a high speed for a longperiod of time without frequently changing the photoreceptor.

[0044] Briefly these objects and other objects of the present inventionas hereinafter will become more readily apparent can be attained by aphotoreceptor which includes an electroconductive substrate, and atleast a photosensitive layer located overlying the substrate, whereinthe photosensitive layer includes a diamine compound having thefollowing formula (1):

[0045] wherein R1 and R2 independently represent a substituted orunsubstituted alkyl group, or a substituted or unsubstituted aromatichydrocarbon group, wherein at least one of R1 and R2 is a substituted orunsubstituted aromatic hydrocarbon group and R1 and R2 optionally sharebond connectivity to form a substituted or unsubstituted ring includinga nitrogen atom; and Ar represents a substituted or unsubstitutedaromatic hydrocarbon group.

[0046] Alternatively, the outermost layer of the photoreceptor includesat least one of an organic compound having an acid value of from 10 to700 mgKOH/g and the diamine compound having formula (1).

[0047] The outermost layer is defined as the layer furthest away fromthe substrate. The photosensitive layer can be the outermost layer.“Overlying” can include direct contact and allow for intermediatelayers.

[0048] The outermost layer may be the photosensitive layer, or anoutermost layer of the photosensitive layer when the photosensitivelayer is constituted of plural layers.

[0049] Alternatively, the outermost layer may be a protective layerformed overlying the photosensitive layer.

[0050] The organic compound having an acid value of from 10 to 700mgKOH/g is preferably a polycarboxylic acid. As the polycarboxylic acid,polyester resins, acrylic resins, copolymers including one or more unitsof the polyester resins and acrylic resins, and mixtures thereof, whichinclude carboxyl group, can be preferably used. The polycarboxylic acidis preferably used together with a fatty acid.

[0051] The filler is preferably an inorganic pigment. The inorganicpigment preferably includes a metal oxide. The inorganic pigmentpreferably has a pH not less than 5 and/or a dielectric constant notless than 5. In addition, the filler preferably has an average primaryparticle diameter of from 0.01 to 0.5 μm.

[0052] The outermost layer preferably includes a charge transportmaterial. The charge transport material is preferably a charge transportpolymer material. The outermost layer preferably includes at least oneof polycarbonate resins and polyarylate resins. The outermost layerpreferably includes an antioxidant. The antioxidant is preferably one ofhydroquinone compounds and hindered amine compounds.

[0053] As another aspect of the present invention, an image formingmethod is provided which includes charging the photoreceptor mentionedabove; irradiating the charged photoreceptor with imagewise light toform an electrostatic latent image on the photoreceptor; developing theelectrostatic latent image with a developer including a toner to form atoner image on the photoreceptor; and transferring the toner image on areceiving material.

[0054] As yet another aspect of the present invention, an image formingapparatus is provided which includes a photoreceptor; a chargerconfigured to charge the photoreceptor; a light irradiator configured toirradiate the charged photoreceptor with imagewise light to form anelectrostatic latent image on the photoreceptor; an image developerconfigured to develop the electrostatic latent image with a developer toform a toner image on the photoreceptor; and a transferring deviceconfigured to transfer the toner image onto a receiving material. Thelight irradiator preferably includes a laser diode (LD) or a lightemitting diode (LED) as a light source.

[0055] As a further aspect of the present invention, a process cartridgeis provided which includes the photoreceptor and at least one of acharger, a light irradiator, an image developer, a transfer device, acleaner configured to clean the surface of the photoreceptor, and adischarger configured to discharge the charges remaining on thephotoreceptor after the image transferring process.

[0056] As a still further aspect of the present invention, a method formanufacturing the photoreceptor is provided which includes the steps ofcoating an outermost layer coating liquid including at least a solvent,a filler, an organic compound having an acid value of from 10 to 700mgKOH/g, a compound having formula (1) and an antioxidant, preferablyselected from the group consisting of hydroquinone compounds andhindered amine compounds.

[0057] These and other objects, features and advantages of the presentinvention will become apparent upon consideration of the followingdescription of the preferred embodiments of the present invention takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Various other objects, features and attendant advantages of thepresent invention will be more fully appreciated as the same becomesbetter understood from the detailed description when considered inconnection with the accompanying drawings in which like referencecharacters designate like corresponding parts throughout and wherein:

[0059] FIGS. 1 to 5 are schematic views illustrating the cross sectionsof typical embodiments of the photoreceptor of the present invention;

[0060]FIG. 6 is a schematic view illustrating an embodiment of the imageforming apparatus of the present invention and for explaining the imageforming method of the present invention;

[0061]FIG. 7 is a schematic view illustrating another embodiment of theimage forming apparatus of the present invention and for explaining theimage forming method of the present invention;

[0062]FIG. 8 is a schematic view illustrating an embodiment of theprocess cartridge of the present invention; and

[0063]FIG. 9 is an X-ray diffraction spectrum of the titanylphthalocyanine for use in the photoreceptor of the present application.

DETAILED DESCRIPTION OF THE INVENTION

[0064] The photoreceptor of the present invention includes anelectroconductive substrate, and at least a photosensitive layer locatedwhich is located overlying the substrate and which includes a compoundhaving the above-mentioned formula (1). Alternatively, the outermostlayer of the photoreceptor (i.e., the layer furthest away from thesubstrate) includes a filler, an organic compound having an acid valueof from 10 to 700 mgKOH/g and a compound having formula (1). Thephotoreceptor of the present invention will be explained referring todrawings.

[0065]FIG. 1 is a schematic view illustrating the cross section of anembodiment of the photoreceptor of the present invention.

[0066] In FIG. 1, a single-layer photosensitive layer 33 including acharge generation material (hereinafter a CGM) and a charge transportmaterial (hereinafter a CTM) as main components is formed on anelectroconductive substrate 31. The photosensitive layer 33 furtherincludes a compound having formula (1). Alternatively, when thephotosensitive layer 33 is an outermost layer of this photoreceptor, thelayer 33 includes a filler, an organic compound having an acid value offrom 10 to 700 mgKOH/g and a compound having formula (1) as well as theCGM and CTM.

[0067]FIG. 2 is a schematic view illustrating the cross section ofanother embodiment of the photoreceptor of the present invention.

[0068] In FIG. 2, a charge generation layer (hereinafter a CGL) 35including a CGM as a main component and a, charge transport layer(hereinafter a CTL) 37 including a CTM as a main component are overlaidon an electroconductive substrate 31 in this order.

[0069] The CTL 37 includes a compound having formula (1). Alternatively,when the CTL 37 is an outermost layer of this photoreceptor, the CTLincludes a filler, an organic compound having an acid value of from 10to 700 mgKOH/g and a compound having formula (1) as well as the CTM. Thefiller may be included uniformly in the CTL 37 or included such that theconcentration of the filler increases in the upward direction of the CTL37.

[0070]FIG. 3 is a schematic view illustrating the cross section of yetanother embodiment of the photoreceptor of the present invention.

[0071] In FIG. 3, a photosensitive layer 33 which includes a CGM and aCTM as main components is formed on an electroconductive substrate 31,and a protective layer 39 is formed on the photosensitive layer 33. Thephotosensitive layer 33 includes a compound having formula (1).Alternatively, the protective layer 39, which is the outermost layer ofthis photoreceptor, includes at least a filler, an organic compoundhaving an acid value of from 10 to 700 mgKOH/g and a compound havingformula (1).

[0072]FIG. 4 is a schematic view illustrating the cross section of afurther embodiment of the photoreceptor of the present invention.

[0073] In FIG. 4, a CGL 35 including a CGM as a main component and a CTL37 including a CTM as a main component are overlaid on anelectroconductive substrate 31 in this order. In addition, a protectivelayer 39 is formed on the CTL 37. The CTL 37 includes a compound havingformula (1). Alternatively, the protective layer 39, which is theoutermost layer of the photoreceptor, includes at least a filler, anorganic compound having an acid value of from 10 to 700 mgKOH/g and acompound having formula (1).

[0074]FIG. 5 is a schematic view illustrating the cross section of astill further embodiment of the photoreceptor of the present invention.

[0075] In FIG. 5, a CTL 37 including a CTM as a main component and a CGL35 including a CGM as a main component are overlaid on anelectroconductive substrate 31 in this order. In addition, a protectivelayer 39 is formed on the CGL 35. The CTL 37 includes a compound havingformula (1). Alternatively, the protective layer 39, which is theoutermost layer of this photoreceptor, includes at least a filler, anorganic compound having an acid value of from 10 to 700 mgKOH/g and acompound having formula (1).

[0076] Suitable materials for use as the electroconductive substrate 31include materials having a volume resistance not greater than 10¹⁰ Ω·cm.Specific examples of such materials include plastic cylinders, plasticfilms or paper sheets, on the surface of which a metal such as aluminum,nickel, chromium, nichrome, copper, gold, silver, platinum and the like,or a metal oxide such as tin oxides, indium oxides and the like, isdeposited or sputtered. In addition, a plate of a metal such asaluminum, aluminum alloys, nickel and stainless steel can be used. Ametal cylinder can also be used as the substrate 31, which is preparedby tubing a metal such as aluminum, aluminum alloys, nickel andstainless steel by a method such as impact ironing or direct ironing,and then subjecting the surface of the tube to cutting, super finishing,polishing and the like treatments. Further, endless belts of a metalsuch as nickel, stainless steel and the like, which have been disclosed,for example, in Japanese Laid-Open Patent Publication No. 52-36016, canalso be used as the substrate 31.

[0077] Furthermore, substrates, in which a coating liquid including abinder resin and an electroconductive powder is coated on the supportsmentioned above, can be used as the substrate 31. Specific examples ofsuch an electroconductive powder include carbon black, acetylene black,powders of metals such as aluminum, nickel, iron, nichrome, copper,zinc, silver and the like, and metal oxides such as electroconductivetin oxides, ITO and the like. Specific examples of the binder resininclude known thermoplastic resins, thermosetting resins andphoto-crosslinking resins, such as polystyrene, styrene-acrylonitrilecopolymers, styrene-butadiene copolymers, styrene-maleic anhydridecopolymers, polyesters, polyvinyl chloride, vinyl chloride-vinyl acetatecopolymers, polyvinyl acetate, polyvinylidene chloride, polyarylates,phenoxy resins, polycarbonates, cellulose acetate resins, ethylcellulose resins, polyvinyl butyral resins, polyvinyl formal resins,polyvinyl toluene, poly-N-vinyl carbazole, acrylic resins, siliconeresins, epoxy resins, melamine resins, urethane resins, phenolic resins,alkyd resins and the like resins.

[0078] Such an electroconductive layer can be formed by coating acoating liquid in which an electroconductive powder and a binder resinare dispersed or dissolved in a proper solvent such as tetrahydrofuran,dichloromethane, methyl ethyl ketone, toluene and the like solvent, andthen drying the coated liquid.

[0079] In addition, substrates, in which an electroconductive resin filmis formed on a surface of a cylindrical substrate using aheat-shrinkable resin tube which is made of a combination of a resinsuch as polyvinyl chloride, polypropylene, polyesters, polyvinylidenechloride, polyethylene, chlorinated rubber and fluorine-containingresins, with an electroconductive material, can also be used as thesubstrate 31.

[0080] Next, the photosensitive layer of the photoreceptor of thepresent invention will be explained.

[0081] In the photoreceptor of the present invention, the photosensitivelayer may be a single-layered photosensitive layer or a multi-layeredphotosensitive layer.

[0082] At first, the multi-layered photosensitive layer including theCGL 35 and the CTL 37 will be explained.

[0083] The CGL 35 includes a CGM as a main component. In the CGL 35,known charge generation materials can be used. Specific examples of suchCGMs include azo pigments such as monoazo pigments, disazo pigments,asymmetric disazo pigments and trisazo pigments; phthalocyanine pigmentssuch as titanyl phthalocyanine, copperphthalocyanine,vanadylphthalbcyanine, hydroxygallium phthalocyanine and metal freephthalocyanine; perylene pigments, perynone pigments, indigo pigments,pyrrolopyrrole pigments, anthraquinone pigments, quinacridone pigments,quinone type condensed polycyclic compounds, squaric acid type dyes, andthe like pigments and dyes. These CGMs can be used alone or incombination.

[0084] The CGL 35 is typically prepared by coating a CGL coating liquid,which is prepared by dispersing a CGM in a solvent optionally togetherwith a binder resin using a dispersing machine such as ball mills,attritors, sandmills and supersonic dispersion machines, on anelectroconductive substrate and then drying the coated liquid.

[0085] Suitable binder resins, which are optionally used in the CGLcoating liquid, include polyamide, polyurethane, epoxy resins,polyketone, polycarbonate, silicone resins, acrylic resins, polyvinylbutyral, polyvinyl formal, polyvinyl ketone, polystyrene, polysulfone,poly-N-vinylcarbazole, polyacrylamide, polyvinyl benzal, polyester,phenoxy resins, vinyl chloride-vinyl acetate copolymers, polyvinylacetate, polyphenylene oxide, polyamides, polyvinyl pyridine, celluloseresins, casein, polyvinyl alcohol, polyvinyl pyrrolidone, and the likeresins.

[0086] The content of the binder resin in CGL 35 is preferably from 0 to500 parts by weight, and preferably from 10 to 300 parts by weight, per100 parts by weight of the charge generation material included in theCGL 35.

[0087] A binder resin can be mixed before or after the dispersionprocess.

[0088] Suitable solvents for use in the CGL coating liquid includeisopropanol, acetone, methyl ethyl ketone, cyclohexanone,tetrahydrofuran, dioxane, ethyl cellosolve, ethyl acetate, methylacetate, dichloromethane, dichloroethane, monochlorobenzene,cyclohexane, toluene, xylene, ligroin, and the like solvents. Inparticular, ketone type solvents, ester type solvents and ether typesolvents are preferably used. These solvents can be used alone or incombination.

[0089] The CGL coating liquid includes a CGM, a solvent and a binderresin as main components, but may include additives such as sensitizers,dispersants, surfactants and silicone oils.

[0090] The CGL coating liquid can be coated by a coating method such asdip coating, spray coating, bead coating, nozzle coating, spinnercoating and ring coating methods. The thickness of the CGL 35 ispreferably from 0.01 to 5 μm, and more preferably from 0.1 to 2 μm.

[0091] Then the CTL 37 will be explained. The CTL 37 includes a CTM as amain component.

[0092] The CTL 37 can be typically formed by the following method:

[0093] (1) a CTM and a binder resin are dispersed or dissolved in aproper solvent to prepare a CTL coating liquid; and

[0094] (2) the CTL coating liquid is coated and dried to form a CTL.

[0095] The CTL coating liquid may include one or more additives such asplasticizers, leveling agents, antioxidants and the like, if desired.

[0096] CTMs are classified into positive-hole transport materials andelectron transport materials.

[0097] Specific examples of the electron transport materials includeelectron accepting materials such as chloranil, bromanil,tetracyanoethylene, tetracyanoquinodimethane,2,4,7-trinitro-9-fluorenon, 2,4,5,7-tetranitro-9-fluorenon,2,4,5,7-tetanitroxanthone, 2,4,8-trinitrothioxanthone,2,6,8-trinitro-4H-indeno[1,2-b]thiophene-4-one,1,3,7-trinitrodibenzothiphene-5,5-dioxide, benzoquinone derivatives andthe like.

[0098] In addition, the following compounds can be used as the electrontransport material.

[0099] wherein R1, R2 and R3 independently represent a hydrogen atom, ahalogen atom, a substituted or unsubstituted alkyl group, an alkoxygroup or a substituted or unsubstituted phenyl group.

[0100] wherein R1 and R2 independently represent a hydrogen atom, asubstituted or unsubstituted alkyl group, or a substituted orunsubstituted phenyl group.

[0101] wherein R1, R2 and R3 independently represent a hydrogen atom, ahalogen atom, a substituted or unsubstituted alkyl group, an alkoxygroup or a substituted or unsubstituted phenyl group.

[0102] wherein R1 represents a substituted or unsubstituted alkyl group,or a substituted or unsubstituted aromatic hydrocarbon group; R2represents a substituted or unsubstituted alkyl group, a substituted orunsubstituted aromatic hydrocarbon group, or the following group:

—O—R³

[0103] wherein R³represents a substituted or unsubstituted alkyl group,or a substituted or unsubstituted aromatic hydrocarbon group.

[0104] Specific examples of the positive-hole transport materialsinclude known materials such as poly-N-carbazole and its derivatives,poly-y-carbazolylethylglutamate and its derivatives, pyrene-formaldehydecondensation products and their derivatives, polyvinyl pyrene, polyvinylphenanthrene, polysilane, oxazole derivatives, oxadiazole derivatives,imidazole derivatives, monoarylamines, diarylamines, triarylamines,stilbene derivatives, α-phenyl stilbene derivatives, benzidinederivatives, diarylmethane derivatives, triarylmethane derivatives,9-styrylanthracene derivatives, pyrazoline derivatives, divinyl benzenederivatives, hydrazone derivatives, indene derivatives, butadienederivatives, pyrene derivatives, bisstilbene derivatives, enaminederivatives, and the like.

[0105] In addition, the following compounds can also be used as thepositive-hole transport material.

[0106] wherein R1 represents a methyl group, an ethyl group, a2-hydroxyethyl group or a 2-chlorethyl group; and R2 represents a methylgroup, an ethyl group, a benzyl group or a phenyl group; and R3represents a hydrogen atom, a chlorine atom, a bromine atom, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, a dialkylamino group or a nitro group.

[0107] Specific examples of the compounds include9-ethylcarbazole-3-aldehyde-1-methyl-1-phenylhydrazone,9-ethylcarbazole-3-aldehyde-1-benzyl-1-phenylhydrazone,9-ethylcarbazole-3-aldehyde-1,1-diphenylhydrazone, etc.

[0108] wherein Ar represents a naphthalene ring, an anthracene ring, apyrene ring, which rings may be substituted, a pyridine ring, a furanring or thiophene ring; and R represents an alkyl group, a phenyl groupor a benzyl group.

[0109] Specific examples of the compounds include4-diethylaminostyryl-β-aldehyde-1-methyl-1-phenylhydrazone,4-methoxynaphthalene-1-aldehyde-1-benzyl-1-phenylhydrazone, etc.

[0110] wherein R1 represents an alkyl group, a benzyl group, a phenylgroup or a naphthyl group; R2 represents a hydrogen atom, an alkyl grouphaving 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms,a dialkylamino group, diaralkylamino group or a substituted orunsubstituted diarylamino group; n is an integer of from 1 to 4, whereinwhen n is not less than 2, R2 may be the same or different from eachother; and R3 represents a hydrogen atom or a methoxy group.

[0111] Specific examples of the compounds include4-methoxybenzaldehyde-1-methyl-1-phenylhydrazone,2,4-dimethoxybenzaldehyde-1-benzyl-1-phenylhydrazone,4-diethylaminobenzaldehyde-1,1-diphenylhydrazone,4-methoxybenzaldehyde-1-(4-methoxy)phenylhydrazone,4-diphenylaminobenzaldehyde-1-benzyl-1-phenylhydrazone,4-benzylaminobenzaldehyde-1,1-diphenylhydrazone, etc.

[0112] wherein R1 represents an alkyl group having 1 to 11 carbon atoms,a substituted or unsubstituted phenyl group or a heterocyclic ringgroup; each of R2 and R3 represents a hydrogen atom, an alkyl grouphaving 1 to 4 carbon atoms, a hydroxyalkyl group, a chloroalkyl group ora substituted or unsubstituted aralkyl group, wherein R2 and R3optionally share bond connectivity to form a heterocyclic ring groupincluding a nitrogen atom; and each of R4 represents a hydrogen atom, analkyl group having 1 to 4 carbon atoms, an alkoxy group or a halogenatom.

[0113] Specific examples of the compounds include1,1-bis(4-dibenzylaminophenyl)propane,tris(4-diethylaminophenyl)methane,2,2′-dimethyl-4,4′-bis(diethylamino)-triphenylmethane, etc.

[0114] wherein R represents a hydrogen atom or a halogen atom; and Arrepresents a substituted or unsubstituted phenyl group, a naphthylgroup, an anthryl group or a carbazolyl group.

[0115] Specific examples of the compounds include9-(-diethylaminostyryl)anthracene,9-bromo-10-(4-diethylaminostyryl)aminoanthracene, etc.

[0116] wherein R1 represents a hydrogen atom, a halogen atom, a cyanogroup, an alkoxy group having 1 to 4 carbon atoms or a alkyl grouphaving 1 to 4 carbon atoms; and Ar represents a group having one of thefollowing formulae:

[0117] wherein R2 represents an alkyl group having 1 to 4 carbon atoms;R³ represents a hydrogen atom, a halogen atom, an alkyl group having 1to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms or adialkylamino group; n is 1 or 2, wherein each of R³ may be the same ordifferent from the others when n is 2; and R⁴ and R⁵ independentlyrepresent a hydrogen atom, a substituted or unsubstituted alkyl grouphaving 1 to 4 carbon atoms or a substituted or unsubstituted benzylgroup.

[0118] Specific examples of the compounds include9-(4-dimethylaminobenzylidene)fluorenone,3-(9-fluorenylidene)-9-ethylcarbazole, etc.

[0119] wherein R represents a carbazolyl group, a pyridyl group, athienyl group, an indolyl group, a furyl group, a substituted orunsubstituted phenyl, a substituted or unsubstituted styryl, asubstituted or unsubstituted naphtyl group or a substituted orunsubstituted anthryl group, wherein the substituent thereof is selectedfrom the group consisting of a dialkylamino group, an alkyl group, analkoxy group, a carboxyl group or its ester, a halogen atom, a cyanogroup, an aralkylamino group, a N-alkyl-N-aralkylamino group, an aminogroup, a nitro group and an acethylamino group.

[0120] Specific examples of the compounds include1,2-bis(4-diethylaminostyryl)benzene,1,2-bis(2,4-dimethoxystyryl)benzene, etc.

[0121] wherein R1 represents a lower alkyl group, a substituted orunsubstituted phenyl group or a benzyl group; R2 and R3 independentlyrepresent a hydrogen atom, a lower alkyl group, a lower alkoxy group, ahalogen atom, a nitro group, an amino group or an amino groupsubstituted with a lower alkyl group or a benzyl group; and n is 1 or 2.

[0122] Specific examples of the compounds include3-styryl-9-ethylcarbazole, 3-(4-methoxystyryl)-9-ethylcarbazol, etc.

[0123] wherein R1 represents a hydrogen atom, an alkyl-group, an alkoxygroup or a halogen atom; R2 and R3 independently represent a substitutedor unsubstituted aromatic hydrocarbon group; R4 represents a hydrogenatom, a lower alkyl group or a substituted or unsubstituted phenylgroup; and Ar represents a substituted or unsubstituted phenyl group ora naphthyl group.

[0124] Specific examples of the compounds include4-diphenylaminostilbene, 4-dibenzylaminostilbene,4-ditolylaminostilbene, 1-(4-diphenylaminostyryl)naphthalene, etc.

[0125] wherein n is 0 or 1; R1 represents a hydrogen atom, an alkylgroup or a substituted or unsubstituted phenyl group; Ar1 represents asubstituted or unsubstituted aromatic hydrocarbon group; R5 representsan alkyl group having from 1 to 4 carbon atoms, or a substituted orunsubstituted aromatic hydrocarbon group, wherein Ar1 and R5 optionallyshare bond connectivity to form a ring; and A represents a 9-anthrylgroup, a substituted or unsubstituted carbazolyl group or a group havingone of the following formulae:

[0126] wherein R 2represents a hydrogen atom, an alkyl group, an alkoxygroup, a halogen atom or a group having a formula of —N(R³)(R⁴), whereinR3 and R4 independently represent a substituted or unsubstitutedaromatic hydrocarbon group, and R³ and R⁴ optionally share bondconnectivity to form a ring; and m is an integer of from 1 to 3, whereinwhen m is not less than 2, each of R² is the same or different from theothers, wherein A and R1 optionally share bond connectivity to form aring together when n is 0.

[0127] Specific examples of the compounds include4′-diphenylamino-α-phenylstilbene,4′-bis(4-methylphenyl)amino-α-phenylstilbene, etc.

[0128] wherein R1, R2 and R3 represent a hydrogen atom, a lower alkylgroup, a lower alkoxy group, a halogen atom or a dialkylamino group; andn is 0 or 1.

[0129] Specific examples of the compounds include1-phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)pyrazoline.

[0130] wherein R1 and R2 independently represent a substituted orunsubstituted alkyl group or a substituted or unsubstituted aromatichydrocarbon group; and A represents a substituted amino group, asubstituted or unsubstituted aromatic hydrocarbon group or an allylgroup.

[0131] Specific examples of the compounds include2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole,2-N,N-diphenylamino-5-(4-diphenylaminophenyl)-1,3,4-oxadiazole,2-(4-dimethylaminophenyl)-5-(4-diethylaminophenyl)-1,3,4-oxadiazole,etc.

[0132] wherein X represents a hydrogen atom, a lower alkyl group or ahalogen atom; R represents a substituted or unsubstituted alkyl group ora substituted or unsubstituted aromatic hydrocarbon group; and Arepresents a substituted amino group, or a substituted or unsubstitutedaromatic hydrocarbon group.

[0133] Specific examples of the compounds include2-N,N-diphenylamino-5-(N-ethylcarbazole-3-yl)-1,3,4-oxadiazole,2-(4-diethylaminophenyl)-5-(N-ethylcarbazole-3-yl)-1,3,4-oxadiazole,etc.

[0134] wherein R1 represents a lower alkyl group, a lower alkoxy groupor a halogen atom; R2 and R3 independently represent a hydrogen atom, alower alkyl group, a lower alkoxy group or a halogen atom; and k, m andn is independently 0 or an integer of from 1 to 4.

[0135] Specific examples of the compounds includeN,N′-diphenyl-N,N′-bis(3-methylhenyl)-[1,1′-biphenyl]-4,4′-diamine,3,3′-dimethyl-N,N,N′,N′-tetrakis(4-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine,etc.

[0136] wherein R1, R3 and R4 independently represent a hydrogen atom, anamino group, an alkoxy group, a thioalkoxy group, an aryloxy group, amethylenedioxy group, a substituted or unsubstituted alkyl group, ahalogen atom or a substituted or unsubstituted aromatic hydrocarbongroup; R2 represents a hydrogen atom, an alkoxy-group, a substituted orunsubstituted alkyl group or a halogen atom; and j, k, m and n areindependently an integer of from 1 to 4, wherein each of R1, R2, R3 andR4 may be the same or different from the others when j, k, m and n arean integer of from 2 to 4.

[0137] Specific examples of the compounds include4′-methoxy-N,N-diphenyl-[1,1′-biphenyl]-4-amine,4′-methyl-N,N-bis(4-methylphenyl)-[1,1′-biphenyl]-4-amine,4′-methoxy-N,N-bis(4-methylphenyl)-[1,1′-biphenyl]-4-amine,N,N-bis(3,4-dimethylphenyl)-[1,1′-biphenyl]-4-amine, etc.

[0138] wherein Ar represents a condensation polycyclic hydrocarbon grouphaving 18 or less carbon atoms which can have a substituent; and R1 andR2 independently represent a hydrogen atom, a halogen atom, asubstituted or unsubstituted alkyl group, an alkoxy group, or asubstituted or unsubstituted phenyl group and n is 1 or 2.

[0139] Specific examples of the compounds includeN,N-diphenyl-pyrene-1-amine, N,N-di-p-tolyl-pyrene-1-amine,N,N-di(p-tolyl)-naphthylamine, N,N-di(p-tolyl)-1-phenanthrylamine,9,9-dimethyl-2-(di-p-tolylamino)fluorenone,N,N,N′,N′-tetrakis(4-methylphenyl)-phenanthrene-9,10-diamine,N,N,N′,N′-tetrakis(3-methylphenyl)-m-phenylenediamine, etc.

A-CH═CH—Ar—CH═CH-A

[0140] wherein Ar represents a substituted or unsubstituted aromatichydrocarbon group; and A represents

[0141] wherein Ar¹ represents a substituted or unsubstituted aromatichydrocarbon group; and R¹ and R² represent substituted or unsubstitutedalkyl group or a substituted or unsubstituted aromatic hydrocarbongroup.

[0142] Specific examples of the compounds include1,4-bis(4-diphenylaminostyryl)benzene,1,4-bis[4-di(p-tolyl)aminostyryl]benzene, etc.

[0143] wherein Ar represents a substituted or unsubstituted aromatichydrocarbon group; R represents a hydrogen atom, a substituted orunsubstituted alkyl group or a substituted or unsubstituted aromatichydrocarbon group; and n is 0 or 1, and m is 1 or 2, wherein Ar and Roptionally share bond connectivity to form a ring when n is 0 and m is1.

[0144] Specific examples of the compounds include1-(4-diphenylaminostyryl)pyrene, 1-(N,N-di-p-tolyl-4-aminostyryl)pyrene,etc.

[0145] These CTMs can be used alone or in combination.

[0146] Specific examples of the binder resin for use in the CTL 37include known thermoplastic resins and thermosetting resins, such aspolystyrene, styrene-acrylonitrile copolymers, styrene-butadienecopolymers, styrene-maleic anhydride copolymers, polyester, polyvinylchloride, vinyl chloride-vinyl acetate copolymers, polyvinyl acetate,polyvinylidene chloride, polyarylate, phenoxy resins, polycarbonate,cellulose acetate resins, ethyl cellulose resins, polyvinyl butyralresins, polyvinyl formal resins, polyvinyl toluene, poly-N-vinylcarbazole, acrylic resins, silicone resins, epoxy resins, melamineresins, urethane resins, phenolic resins, alkyd resins and the like.

[0147] The content of the CTM in the CTL 37 is preferably from 20 to 300parts by weight, and more preferably from 40 to 150 parts by weight, per100 parts by weight of the binder resin included in the CTL 37. Thethickness of the CTL 37 is preferably not greater than 25 μm in view ofresolution of the resultant images and response (i.e., photosensitivity)of the resultant photoreceptor. In addition, the thickness of the CTL 37is preferably not less than 5 μm in order that the resultantphotoreceptor has a sufficient potential when charged. The lower limitof the thickness changes depending on the image forming system for whichthe photoreceptor is used.

[0148] Suitable solvents for use in the CTL coating liquid includetetrahydrofuran, dioxane, toluene, dichloromethane, monochlorobenzene,dichloroethane, cyclohexanone, methyl ethyl ketone, acetone and the likesolvents. These solvents can be used alone or in combination.

[0149] When the CTL 37 is the outermost layer (i.e., the layer farthestfrom the substrate 31), the CTL 37 includes a filler, an organiccompound having an acid value of from 10 to 700 mgKOH/g, and a compoundhaving the following formula (1):

[0150] wherein R1 and R2 independently represent a substituted orunsubstituted alkyl group, or a substituted or unsubstituted aromatichydrocarbon group, wherein at least one of R1 and R2 is-a substituted orunsubstituted aromatic hydrocarbon group and R1 and R2 can optionallyshare bond connectivity to form a substituted or unsubstituted ringincluding a nitrogen atom; and Ar represents a substituted orunsubstituted aromatic hydrocarbon group.

[0151] As the filler to be added to the outermost layer of thephotoreceptor to improve the abrasion resistance of the photoreceptor,organic fillers and inorganic fillers can be used. Suitable organicfillers include powders of fluorine-containing resins such aspolytetrafluoroethylene, silicone resin powders, amorphous carbonpowders, etc.

[0152] Specific examples of the inorganic fillers include powders ofmetals such as copper, tin, aluminum and indium; metal oxides such assilica, tin oxide, zinc oxide, titanium oxide, alumina, zirconia,indiumoxide, antimonyoxide, bismuth oxide, calcium oxide, tin oxidedoped with antimony, indium oxide doped with tin; metal fluoride such astin fluoride, calcium fluoride and aluminum fluoride; potassiumtitanate, boron nitride, etc.

[0153] Among these fillers, inorganic fillers are preferably usedbecause of having high hardness.

[0154] When the CTL 37 of the photoreceptor having a structure asillustrated in FIG. 2 includes such a filler as mentioned above, theresultant photoreceptor has good durability but the blurred imageproblem and the residual potential increasing problem are caused. Thepresent inventors discover that by including a filler having a highinsulation property in the protective layer, occurrence of the blurredimage problem can be prevented, and in addition by including an organiccompound having an acid value of from 10 to 700 mgKOH/g therein,occurrence of the residual potential increasing problem can beprevented. The residual potential is decreased by using a compoundhaving such a specific acid value. However, improvement in thedispersibility of the filler in the resultant layer, which is caused byaddition of the specific compound, also influences on the decrease ofresidual porential. Since the dispersibility of the filler can beimproved, the light transmittance of the CTL 37 can be improved, andthereby images having uniform image density can be produced, resultingin formation of high quality images. In addition, the abrasionresistance of the photoreceptor can be improved and generation ofcoating defects can also be prevented when the CTL 37 is prepared bycoating.

[0155] Suitable fillers having a high insulation property includefillers having a pH not less than 5 and fillers having a dielectricconstant not less than 5. Specific examples thereof include titaniumoxide, alumina, zinc oxide, zirconium oxide, etc. Fillers having a pHnot less than 5 and fillers having a dielectric constant not less than 5can be used alone and in combination. Further, combinations of one ormore fillers having a pH not less than 5 with one or more fillers havinga pH less than 5, and combinations of one or more fillers having adielectric constant not less than 5 with one or more fillers having adielectric constant less than 5, can also be used.

[0156] Among these fillers, α-alumina having a hexagonal closest packingstructure is preferable because of having good heat stability and goodabrasion resistance. By using α-alumina having a hexagonal closestpacking structure, occurrence of the blurred image problem can beprevented and the abrasion resistance of the photoreceptor can beimproved.

[0157] The surface of these fillers is preferably coated with a surfacetreatment agent to improve dispersion of the fillers. As mentionedabove, when the dispersibility of the filler deteriorates, variousproblems occurs such that the transparency of the resultant layerdecreases, coating defects are produced, and the abrasion resistance ofthe layer deteriorates. Therefore, a photoreceptor having gooddurability and capable of producing high quality images cannot beprepared.

[0158] As the surface treatment agent, known surface treating agents canbe used. However, surface treatment agents, which do not deteriorate theinsulation property of the filler to be treated, are preferably used.

[0159] Suitable surface treatment agents include titanate couplingagents, aluminum coupling agents, zircoaluminate coupling agents, higherfatty acids, etc. In addition, fillers treated with Al₂O₃, TiO₂, ZrO₂,silicones, aluminum stearate or their mixtures can also be preferablyused because dispersion of the fillers can be improved and occurrence ofthe blurred image problem can be prevented.

[0160] When a filler treated with a silane coupling agent is used, theblurred image problem tends to occur. However, by treating a filler witha combination of one or more of the other treating agents with a silanecoupling agent, there is a possibility that the blurred image problemcan be avoided.

[0161] The weight ratio (ST/F) of the surface treatment agent (ST) tothe filler (F) to be coated is from 3 to 30%, and preferable 5 to 20%although the preferable weight ratio changes depending on the averageprimary particle diameter of the filler. When the amount of thetreatment agent is too small, dispersibility of the filler cannot beimproved. To the contrary, when the amount of the treatment agent is toolarge, residual potential of the resultant photoreceptor tends toserious increase.

[0162] The average primary particle diameter of the filler included inthe outermost layer is preferably from 0.01 to 0.5 μm in view of lighttransmittance and abrasion resistance of the resultant outermost layer.Fillers having too small an average primary particle diameter tend tohave poor dispersibility and therefore the abrasion resistance of theresultant photoreceptor deteriorates. To the contrary, when the averageprimary particle diameter is too large, various problems tends to occursuch that the filler precipitates in the coating liquid, and a film of atoner is formed on the photoreceptor.

[0163] The content of the filler in the outermost layer is preferablyfrom 5 to 50% by weight, and more preferably from 10 to 40% by weight.When the content is too low, the abrasion resistance is hardly improved.When the content is too high, the transparency of the resultant CTL 37deteriorates.

[0164] Then the organic compound having an acid value of from 10 to 700mgKOH/g will be explained.

[0165] When an organic filler having an acid value of from 10 to 700mgKOH/g is added together with a filler having a high insulationproperty, it is possible to prevent occurrence of residual potentialincreasing problem which is caused by the filler.

[0166] The acid value of an organic compound is defined as the quantity(in units of milligram) of potassium hydroxide needed for neutralizingfree acids and active carboxyl groups included in 1 mg of the compound.

[0167] Specific examples of the organic compounds having an acid valueof from 10 to 700 mgKOH/g include any known materials such as organicfatty acids and resins having a high acid value, which have an acidvalue of from 10 to 700 mgKOH/g. However, low molecular weight organicacids such as maleic acid, citric acid, tartaric acid and succinic acid,and low molecular weight acceptors tend to deteriorate thedispersibility of the filler, and thereby the residual potentialdecreasing effect cannot be fully produced. Therefore, in order toprevent the occurrence of the residual potential increasing problemwhile improving the dispersibility of the filler in the layer, polymers,resins and copolymers having a relatively low molecular weight can bepreferably used. It is preferable for the compounds to have a linearstructure (i.e., a structure without steric hindrance). In this case, itis important to use a compound which has good affinity for the fillerand the binder resin included in the layer. Compounds having a largesteric hindrance tend to have poor affinity for such fillers and binderresins, and thereby the dispersibility of the filler deteriorates,resulting in occurrence of the above-mentioned problems.

[0168] From this point of view, polycarboxylic acids are preferable asthe organic compounds having such a specific acid value as mentionedabove. Polycarboxylic acids are defined as compounds having two or morecarboxyl group therein. Suitable polycarboxylic acids include polymersand copolymers such as polyester resins, acrylic resins, acryliccopolymers, methacrylic copolymers, styrene/acrylic copolymers, theirderivatives, etc., which have two or more carboxyl groups. Thesecompounds can be used alone or in combination. There is a case wherewhen these compounds are used together with a fatty acid, thedispersibility of the filler, and the residual potential decreasingeffect can be improved.

[0169] In the photoreceptor of the present invention, an organiccompound having an acid value of from 10 to 700 mgKOH/g is used. Morepreferably the acid value of the organic compound is from 30 to 400mgKOH/g. When the acid value is too high, the resultant layer has toolow an electric resistance and thereby the blurred image problem tendsto occur. In contrast, when the acid value is too low, the additioncontent of the compound has to be increased and/or the residualpotential decreasing effect cannot be effectively produced. Namely, whena compound having such a specific acid value is added, it is necessaryto determine the addition amount of the compound in consideration of theacid value of the compound. In this regard, it is not necessarily truethat the more acid value the added compound has, the better residualpotential decreasing effect the compound produces. Specifically, theresidual potential decreasing effect also depends on the ability of thefiller to adsorb the compound.

[0170] The content of the organic compound having an acid value of from10 to 700 mgKOH/g is preferably determined in consideration of the acidvalue thereof and the filler content. For example, when two kinds ofcompounds A and B having an acid value from 10 to 700 mgKOH/g are used,it is preferable that the following relationship is satisfied:

0.1≦Acid Value Equivalent(=A×B/C)≦20

[0171] wherein A and B represent the acid values of the compounds A andB, respectively.

[0172] When the content of the compound having an acid value from 10 to700 mgKOH/g is too high, there is a case where the dispersibility of thefiller deteriorates and the blurred image problem occurs. In contrast,when the content is too low, the dispersibility deteriorates and theresidual potential decreasing effect is insufficiently produced.

[0173] When a filler and a compound having an acid value of from 10 to700 mgKOH/g is contained in the CTL 37, the filler and the compound arepreferably dispersed in an organic solvent using a known dispersingmachine such as ball mills, attritors, sand mills and supersonicdispersing machines. Among these dispersing machines, ball mills arepreferable because of effectively contacting the materials to each otherwhile foreign materials are hardly included in the liquid. As the mediumfor use as the balls of the ball mill, known media such as zirconiaballs, alumina balls, agate balls, etc. can be used. However, in view ofdispersing ability and the residual potential decreasing effect, aluminaballs are preferably used. Zirconia balls tend to be abraded during thedispersion operation, and thereby the residual potential of theresultant photoreceptor seriously increases due to inclusion of thezirconia powder in the coating liquid. When zirconia powder is includedin the coating liquid, the dispersibility of the filler deteriorates,and thereby the filler tends to precipitate in the liquid.

[0174] When alumina balls are used as the dispersing medium, the amountof the alumina powder caused by abrasion of the alumina balls is little.In addition, even when the alumina powder is included in the liquid, theinfluence thereof on the residual potential and the dispersibility ofthe filler is very little. Therefore, alumina balls are preferably usedas the dispersing medium.

[0175] When the coating liquid is prepared, the organic compound havingan acid value of from 10 to 700 mgKOH/g is preferably mixed with afiller before the dispersion process because aggregation of the fillerand precipitation of the filler in the coating liquid can be prevented.The binder resin and a CTM can be mixed with the filler and the organiccompound before the dispersion process. However, there is a case wherethe dispersibility of the filler slightly deteriorates. Therefore, it ispreferable that the binder resin and the CTM are added to the dispersionincluding the filler and the organic compound while being dissolved inan organic solvent.

[0176] Then the compound having formula (1), which is included in thephotosensitive layer and/or in the outermost layer together with thefiller and the organic compound having an acid value of from 10 to 700mgKOH/g will be explained.

[0177] The compound having formula (1) is added to solve the blurredimage problem which tends to be caused by the organic compound having anacid value of from 10 to 700 mgKOH/g. Specifically, the organic compoundhaving such an acid value tends to adsorb oxidizing materials such asozone or NOx generated by chargers or the like used in image formingapparatus. In this case, electric resistance of the outermost layertends to decrease, resulting in occurrence of the blurred image problem.A compound having formula (1) is added to prevent occurrence of theproblem. The reason why the problem can be solved is not yet determinedbut it is considered to be that the substituted amino groups in thecompound prevent the oxidizing materials from generating radicalmaterials. In general, the compounds having formula (1) have a chargetransportability, and therefore the compounds do not serve as chargetraps. Therefore, the compounds do not increase the residual potentialof the resultant photoreceptor.

[0178] The diamine compounds having formula (1) can be easily preparedby a method disclosed by E. Elceand A. S. Hay, Polymer, Vo. 37, No. 9,1745 (1996) incorporated herein by reference. Specifically, a dihalogencompound having the following formula (2) is reacted with a secondaryamine having the following formula (3) at a temperature of from roomtemperature to about 100° C. in the presence of a basic compound:

XH₂C—Ar—CH₂X   (2)

[0179] wherein Ar represents a substituted or unsubstituted aromatichydrocarbon group; and X represents a halogen atom; and

HN(R1)(R2)   (3)

[0180] wherein R1 and R2 independently represent a substituted orunsubstituted alkyl group or a substituted or unsubstituted aromatichydrocarbon group, wherein at least one of R1 and R2 is a substituted orunsubstituted aromatic hydrocarbon group and R1 and R2 can optionallyshare bond connectivity to form a substituted or unsubstituted ringincluding a nitrogen atom.

[0181] Specific examples of the basic materials mentioned above includepotassium carbonate, sodium carbonate, potassium hydroxide, sodiumhydroxide, sodium hydride, sodium methylate, potassium-t-butoxide, etc.Specific examples of the solvent used for the reaction mentioned aboveinclude dioxane, tetrahydrofuran, toluene, xylene, dimethylsulfoxide,N,N-dimethylformamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazoline,acetonitrile, etc.

[0182] Specific examples of the alkyl groups for use in the groups R1and R2 include a methyl group, an ethyl group, a propyl group, a butylgroup, a hexyl group, an undecanyl group, etc. Specific examples of thearomatic hydrocarbon groups include aromatic ring groups such as aphenyl group, a biphenyl group, an anthryl group, a fluorenyl group, anda pyrenyl group; and aromatic heterocylic groups such as a pyridylgroup, a quinolyl group, a thiophenyl group, a furanyl group, a furylgroup, an oxazolyl group, an oxadiazolyl group, a carbazolyl group, etc.These groups can be substituted. Specific examples of the substituentsinclude alkoxy groups such as a methoxy group, an ethoxy group, apropoxy group, a butoxy group; halogen atoms such as a fluorine atom, achlorine atom, a bromine atom, and iodine atom; the above-mentionedaromatic hydrocarbon groups; and heterocylic groups such as pyrrolidinylgroup, a piperidyl group and a piperazyl group. In addition, specificexamples of the heterocyclic groups including a nitrogen atom, which areoptionally prepared when R1 and R2 share bond connectivity, include apyrrolidino group a piperidino group and a pieprazino group.

[0183] Specific examples of the compounds having formula (1) include thecompounds listed in Tables 1 to 3. However, the compounds having formula(1) are not limited thereto. TABLE 1 [Formula (1)]

Comp. No. Ar R1 R2 1

—CH₃

2

—CH₂CH₃

3

—CH₃

4

—CH₂CH₃

5

—CH₂CH₂CH₃

6

—CH₂CH₃

7

8

9

—CH₂CH₃

10

11

—CH₂CH₃

12

—CH₂CH₃

13

14

[0184] TABLE 2 Comp. No. Ar R1 R2 15

—CH₂CH₃

16

—CH₃

17

—CH₂CH₃

18

19

—CH₃

20

—CH₂CH₃

21

22

23

—CH₂CH₃

24

25

—CH₂CH₃

26

—CH₃

27

28

—CH₂CH₃

[0185] TABLE 3 Comp. No. Ar R1 R2 29

—CH₃

30

—CH₂CH₃

31

—CH₂CH₃

32

—CH₂CH₃

33

—CH₂CH₃

34

35

36

37

[0186] The content of the compound having formula (1) in the layer ispreferably from 0.01 to 150% by weight based on the weight of the binderresin included in the layer. When the content is too low, the resistanceto oxidizing materials of the resultant layer is poor. In contrast, whenthe content is too high, the film strength of the resultant layerdeteriorates, resulting in deterioration of the abrasion resistance ofthe layer.

[0187] When a coating liquid including a compound having formula (1) anda compound having an acid value of from 10 to 700 mgKOH/g is preserved,an antioxidant is preferably added to the coating liquid to preventformation of salts of the compounds. When the salts are formed, not onlythe coating liquid is colored, but also the resultant photoreceptorcauses the residual potential increasing problem. The coloring of thecoating liquid, which is caused by formation of salts of the compounds,is mainly due to the specific structure of the compound having formula(1). The present inventors discover that by including one or more of thebelow-mentioned specific antioxidants in the coating liquid, thepreservation property of the coating liquid can be improved.

[0188] As the antioxidant, known antioxidants can be used, buthydroquinone-based antioxidants and hindered amine-based antioxidantsare effective.

[0189] The object of using an antioxidant in the coating liquid isdifferent from that of using the antioxidants mentioned below for use inthe layers constituting the photoreceptor, and is to protect thecompound having formula (1) in the coating liquid. Therefore, in thiscase the antioxidant is preferably added to the coating liquid beforethe compound having formula (1) is added to the coating liquid. Thecontent of the antioxidant is preferably 0.1 to 200% by weight based onthe compound having an acid value of from 10 to 700 mgKOH/g to impartgood preservability to the resultant coating liquid.

[0190] The CTL 37 preferably includes a charge transport polymer, whichhas both a binder resin function and a charge transport function,because the resultant CTL has good abrasion resistance and the resultantphotoreceptor can produce high quality image. Known charge transportmaterials can be used for the CTL 37. In particular, polycarbonateresins having a triarylamine group in their main chain and/or side chainare preferably used. In particular, charge transport polymers having thefollowing formulae of from (4) to (13) are preferably used:

[0191] wherein R₁, R₂ and R₃ independently represent a substituted orunsubstituted alkyl group, or a halogen atom; R₄ represents a hydrogenatom, or a substituted or unsubstituted alkyl group; R₅, and R₆independently represent a substituted or unsubstituted aromatichydrocarbon group; r, p and q independently represent 0 or an integer offrom 1 to 4; k is a number of from 0.1 to 1.0 and j is a number of from0 to 0.9; n is an integer of from 5 to 5000; and X represents a divalentaliphatic group, a divalent alicyclic group or a divalent group havingthe following formula (14):

[0192] wherein R₁₀₁ and R₁₀₂ independently represent a substituted orunsubstituted alkyl group, a substituted or unsubstituted aromatichydrocarbon group, or a halogen atom; t and m represent 0 or an integerof from 1 to 4; v is 0 or 1; and Y represents a linear alkylene group, abranched alkylene group, a cyclic alkylene group, —O—, —S—, —SO—, —SO₂—,—CO—, —CO—O-Z-O—CO— (Z represents a divalent aliphatic group), or agroup having the following formula (15):

[0193] wherein a is an integer of from 1 to 20; b is an integer of from1 to 2000; and R₁₀₃ and R₁₀₄ independently represent a substituted orunsubstituted alkyl group, or a substituted or unsubstituted aromatichydrocarbon group, wherein each of R₁₀₁, R₁₀₂, R₁₀₃ and R₁₀₄ may be thesame or different from the others.

[0194] wherein R₇ and R₈ independently represent a substituted orunsubstituted aromatic hydrocarbon group; Ar₁, Ar₂ and Ar₃ independentlyrepresent an arylene group; and X, k, j and n are defined above informula (4).

[0195] wherein R₉ and R₁₀ independently represent a substituted orunsubstituted aromatic hydrocarbon group; Ar₄, Ar₅ and Ar₆ independentlyrepresent an arylene group; and X, k, j and n are defined above informula (4).

[0196] wherein R₁₁ and R₁₂ independently represent a substituted orunsubstituted aromatic hydrocarbon group; Ar₇, Ar₈ and Ar₉ independentlyrepresent an arylene group; p is an integer of from 1 to 5; and X, k, jand n are defined above in formula (4).

[0197] wherein R₁₃ and R₁₄ independently represent a substituted orunsubstituted aromatic hydrocarbon group; Ar₁₀, Ar₁₁ and Ar₁₂independently represent an arylene group; X₁ and X₂ independentlyrepresent a substituted or unsubstituted ethylene group, or asubstituted or unsubstituted vinylene group; and X, k, j and n aredefined above in formula (4).

[0198] wherein R₁₅, R₁₆, R₁₇ and R₁₈ independently represent asubstituted or unsubstituted aromatic hydrocarbon group; Ar₁₃, Ar₁₄,Ar₁₅ and Ar₁₆ independently represent an arylene group; Y₁, Y₂ and Y₃independently represent a substituted or unsubstituted alkylene group, asubstituted or unsubstituted cycloalkylene group, a substituted orunsubstituted alkylene ether group, an oxygen atom, a sulfur atom, or avinylene group; u, v and w independently represent 0 or 1; and X, k, jand n are defined above in formula (4).

[0199] wherein R₁₉ and R₂₀ independently represent a hydrogen atom, orsubstituted or unsubstituted aromatic hydrocarbon group, and R₁₉ and R₂₀optionally share bond connectivity to form a ring; Ar₁₇, Ar₁₈ and Ar₁₉independently represent an arylene group; and X, k, j and n are definedabove in formula (4).

[0200] wherein R₂₁ represents a substituted or unsubstituted aromatichydrocarbon group; Ar₂₀, Ar₂₁, Ar₂₂ and Ar₂₃ independently represent anarylene group; and X, k, j and n are defined above in formula (4).

[0201] wherein R₂₂, R₂₃, R₂₄ and R₂₅ independently represent asubstituted or unsubstituted aromatic hydrocarbon group; Ar₂₄, Ar₂₅,Ar₂₆, Ar₂₇ and Ar₂₈ independently represent an arylene group; and X, k,j and n are defined above in formula (4).

[0202] wherein R₂₆ and R₂₇ independently represent a substituted orunsubstituted aromatic hydrocarbon group; Ar₂₉, Ar₃₀ and Ar₃₁independently represent an arylene group; and X, k, j and n are definedabove in formula (4).

[0203] In addition, polymers having the following formula can also beused as the charge transport polymer material.

[0204] wherein Ar1, Ar2, Ar3, Ar4 and Ar5 independently represent asubstituted or unsubstituted aromatic hydrocarbon group; Z represents anaromatic hydrocarbon group or a group —Ar6-Za-Ar6-, wherein Ar6represents a substituted or unsubstituted aromatic hydrocarbon group, Zarepresents O, S or an alkylene group; R and R′ independently represent alinear or branched alkylene group; m is 0 or 1; and X, k, j and n aredefined above in formula (4).

[0205] The CTL layer is typically formed by coating a CTL coating liquidby a known coating method such as dip coating methods, spray coatingmethods, bead coating methods, nozzle coating methods, spinner coatingmethods and ring coating methods. When a filler is included in anoutermost layer, the filler can be included in the layer such that theconcentration is uniform at any portion of the layer. However, theconcentration of the filler is preferably changed by gradation such thatthe concentration in the surface portion of the layer is higher thanthat in the bottom portion of the layer. Alternatively, it is possiblethat the outermost layer includes plural layers and the concentration ofthe filler in a layer is changed such that the upper layer has a higherfiller concentration.

[0206] Next, the single-layered photosensitive layer 33 (as illustratedin FIGS. 1 and 3) will be explained. The photosensitive layer 33 can beformed by coating a coating liquid in which a CGM, a CTL and a binderresin are dissolved or dispersed in a proper solvent, and then dryingthe coated liquid. The photosensitive layer 33 preferably includes acompound having formula (1). As the CGM and CTM, the CGMs and CTLsmentioned above for use in the CGL 35 and CTL 37 can be used. Ifdesired, additives such as plasticizers, leveling agents andantioxidants can be included in the layer.

[0207] Suitable binder resins for use in the single-layeredphotosensitive layer 33 include the resins mentioned above for use inthe CTL 37. In addition, the resins mentioned above for use in the CGL35 can be used in combination with the binder resins for use in the CTL37. In addition, the charge transport polymer materials for use in theCTL 37 can be preferably used as a binder resin.

[0208] The content of the CGM is preferably from 5 to 40 parts by weightper 100 parts by weight of the binder resin included in thesingle-layered photosensitive layer 33. The content of the CTM ispreferably from 0 to 190 parts, and more preferably from 50 to 150 partsby weight, per 100 parts by weight of the binder resin included in thesingle-layered photosensitive layer 33.

[0209] The single-layered photosensitive layer 33 can be formed bycoating a coating liquid in which a CGM, a binder and a CTM aredissolved or dispersed in a solvent such as tetrahydrofuran, dioxane,dichloroethane and cyclohexane by a coating method such as dip coating,spray coating, bead coating and ring coating.

[0210] The thickness of the photosensitive layer 33 is preferably fromabout 5 to about 25 μm.

[0211] When the single-layered photosensitive layer 33 is the outermostlayer, the photosensitive layer 33 further includes a filler, an organiccompound having an acid value of from 10 to 700 mgKOH/g, and a compoundhaving formula (1).

[0212] In this case, the filler concentration can also be changed bygradation in the single-layered photosensitive layer 33 as mentionedabove.

[0213] In the photoreceptor of the present invention, an undercoat layermay be formed between the substrate 31 and the photosensitive layer(i.e., the photosensitive layer 33 in FIGS. 1 and 3, the CGL 35 in FIGS.2 and 4, and the CTL in FIG. 5).

[0214] The undercoat layer typically includes a resin as a maincomponent. Since a photosensitive layer is typically formed on theundercoat layer by coating a liquid including an organic solvent, theresin in the undercoat layer preferably has good resistance to generalorganic solvents.

[0215] Specific examples of such resins include water-soluble resinssuch as polyvinyl alcohol resins, casein and polyacrylic acid sodiumsalts; alcohol soluble resins such as nylon copolymers andmethoxymethylated nylon resins; and thermosetting resins capable offorming a three-dimensional network such as polyurethane resins,melamine resins, alkyd-melamine resins, epoxy resins and the like.

[0216] The undercoat layer may include a fine powder of metal oxidessuch as titanium oxide, silica, alumina, zirconium oxide, tin oxide andindium oxide to prevent occurrence of moire in the resultant images andto decrease residual potential of the resultant photoreceptor.

[0217] The undercoat layer can also be formed by coating a coatingliquid using a proper solvent and a proper coating method mentionedabove for use in the photosensitive layer.

[0218] The undercoat layer may be formed using a silane coupling agent,titanium coupling agent or a chromium coupling agent.

[0219] In addition, a layer of aluminum oxide which is formed by ananodic oxidation method and a layer of an organic compound such aspolyparaxylylene or an inorganic compound such as SiO, SnO₂, TiO₂, ITOor CeO₂ which is formed by a vacuum evaporation method is alsopreferably used as the undercoat layer.

[0220] The thickness of the undercoat layer is preferably 0 to 5 μm.

[0221] In the photoreceptor of the present invention, the protectivelayer 39 is preferably formed as an outermost layer as illustrated inFIGS. 3-5 to protect the photosensitive layer.

[0222] Specific examples of the binder resin for use in the protectivelayer 39 include ABS resins, ACS resins, olefin-vinyl monomercopolymers, chlorinated polyether, aryl resins, phenolic resins,polyacetal, polyamide, polyamideimide, polyacrylate, polyallysulfone,polybutylene, polybutylene terephthalate, polycarbonate,polyethersulfone, polyethylene, polyethylene terephthalate, polyimide,acrylic resins, polymethylpentene, polypropylene, polyphenyleneoxide,polysulfone, polystyrene, polyarylate, AS resins, butadiene-styrenecopolymers, polyurethane, polyvinyl chloride, polyvinylidene chloride,epoxy resins, etc. Among these resins, polycarbonate resins andpolyarylate are preferably used because the resins have good fillerdispersing ability, good residual potential decreasing ability and goodcoating defects and the resins hardly cause coating defects.

[0223] When the photoreceptor has such a structure as illustrated inFIGS. 4 and 5, the materials and constitution of the CGL 35 and CTL 37are the same as those of the CGL 35 and CTL 37 of the photoreceptorillustrated in FIG. 2. In addition, when the photoreceptor has such astructure as illustrated in FIG. 3, the materials and constitution ofthe single-layered photosensitive layer 33 are the same as those of thephotosensitive layer 33 of the photoreceptor illustrated in FIG. 1.

[0224] The protective layer 39 includes a filler to improve the abrasionresistance of the photoreceptor. In addition, the protective layerfurther includes an organic compound having an acid value of from 10 to700 mgKOH/g and a compound having formula (1).

[0225] Specific examples of the filler for use in the protective layerinclude the fillers mentioned above for use in the CTL 37. Among thefillers, inorganic fillers are preferably used in view of abrasionresistance. In particular, metal oxides having a pH not less than 5and/or a dielectric constant not less than 5 are more preferably usedbecause of having good blurred image preventing ability. Specificexamples of the metal oxides include titanium oxide, alumina, zincoxide, zirconium oxide, etc. As mentioned above, these fillers can beused alone or in combination. In addition, combinations of a fillerhaving a pH less than 5 and a filler having a pH not less than 5, orcombinations of a filler having a dielectric constant less than 5 and afiller having a dielectric constant not less than 5, can also be used.Among these fillers, α-alumina is even more preferably used becauseα-alumina has high insulating property, good heat stability and highhardness (i.e., good abrasion resistance), and hardly causeagglomeration.

[0226] The surface of the filler used for the protective layer ispreferably coated with a surface treatment agent to improvedispersibility of the filler. The surface treatment agents mentionedabove for use in the CTL 37 can also be used for the protective layer39. The surface treatment agents can be used alone or in combination.

[0227] The weight ratio (ST/F) of the surface treatment agent (ST) tothe filler (F) to be coated is from 3 to 30%, and preferable 5 to 20%although the preferable weight ratio changes depending on the averageprimary particle diameter of the filler. When the amount of thetreatment agent is too small, dispersibility of the filler cannot beimproved. To the contrary, when the amount of the treatment agent is toolarge, residual potential of the resultant photoreceptor tends toserious increase.

[0228] The average primary particle diameter of the filler included inthe outermost layer is preferably from 0.01 to 0.5 μm in view of lighttransmittance and abrasion resistance of the protective layer. Fillershaving too small an average primary particle diameter tend to have poordispersibility and therefore the abrasion resistance of the resultantphotoreceptor deteriorates. In contrast, when the average primaryparticle diameter is too large, various problems occurs such that thefiller tends to precipitate in the coating liquid, and a film of a tonertends to be formed on the photoreceptor.

[0229] The content of the filler in the protective layer is preferablyfrom 0.1 to 50% by weight, and more preferably from 5 to 30% by weight.When the content is too low, good abrasion resistance cannot be impartedto the protective layer. When the content is too high, the transparencyof the resultant protective layer 39 deteriorates.

[0230] The organic compounds having an acid value of from 10 to 700mgKOH/g mentioned above for use in the CTL 37 can also be used for theprotective layer 39. Similarly to the case of the CTL 37, polycarboxylicacids are preferably used for the protective layer.

[0231] Polycarboxylic acids are defined as compounds having two or morecarboxyl group therein. Suitable polycarboxylic acids for use in theprotective layer include polymers such as polyester resins, acrylicresins, acrylic copolymers, methacrylic copolymers, styrene/acryliccopolymers, their derivatives, etc., which have a plurality of carboxylgroups therein. These compounds can be used alone or in combination.There is a case where when these compounds are used in combination, thedispersibility of the filler can be improved.

[0232] It is preferable that the acid value of the organic compoundincluded in the protective layer is from 30 to 400 mgKOH/g. When theacid value is too high, the resultant images tend to be blurred becausethe resistance of the protective layer decreases. In contrast, when theacid value is too low, the addition content of the compound has to beincreased and/or the residual potential decreasing effect cannot beeffectively produced. Namely, when a compound having such a specificacid value is added, it is necessary to determine the addition amount ofthe compound in consideration of the acid value of the compound. In thisregard, it is not necessarily true that the more acid value the addedcompound has, the better residual potential decreasing effect thecompound can produce. Specifically, the residual potential decreasingeffect also depends on the ability of the filler to adsorb the compound.

[0233] The content of the organic compound having an acid value of from10 to 700 mgKOH/g is preferably determined in consideration of the acidvalue thereof and the filler content. For example, when two kinds ofcompounds A and B having an acid value from 10 to 700 mgKOH/g are used,it is preferable that the following relationship is satisfied:

0.1≦(A×B/C)≦20

[0234] wherein A and B represent the acid values of the compounds A andB, respectively

[0235] When the content of the compound having an acid value from 10 to700 mgKOH/g is too high, there is a case where the dispersibility of thefiller deteriorates and the blurred image problem occurs. In contrast,when the content is too low, the dispersibility deteriorates and theresidual potential decreasing effect is insufficiently produced.

[0236] As the compound having formula (1) used for improving theoxidizing-gas resistance of the protective layer, the compoundsmentioned above for use in the CTL 37 serving as an outermost layer canalso be used.

[0237] Suitable organic solvents for use in the protective layer coatingliquid include tetrahydrofuran, dioxane, toluene, dichloromethane,monochlorobenzene, dichloroethane, cyclohexanone, methyl ethyl ketone,acetone, etc. A solvent having high viscosity is preferable when acoating liquid is prepared, but a volatile solvent is preferable in viewof drying of the coating liquid. Therefore it is preferable to select asolvent fulfilling such requirements. It is preferable to use a mixturesolvent if there is no solvent fulfilling such requirements. This methodis useful for improving dispersion stability of the filler used and forpreventing occurrence of the residual potential increasing problem.

[0238] In addition, the protective layer 39 preferably includes a CTM ora charge transport polymer material to decrease the residual potentialand improve the image qualities.

[0239] The protective layer is typically formed by the following method.At least a filler, an organic compound having an acid value of from 10to 700 mgKOH/g, and a compound having formula (1) are dispersed in anorganic solvent using a dispersing machine such as ball mills,attritors, sand mills and supersonic dispersing machines. Among thesedispersing machines, ball mills are preferable because of effectivelycontacting the materials to each other while foreign materials arehardly included in the liquid.

[0240] Suitable dispersing media for use as the balls of the ball millsinclude known media such as zirconia, alumina, agate, glass, etc. Amongthese media, alumina is preferable in view of dispersion efficiency andresidual potential decreasing effect. When zirconia is used as adispersing element, zirconia is abraded during the dispersion process,resulting in contamination of zirconia in the coating liquid, andthereby residual potential of the resultant photoreceptor tends toincrease and the filler tends to easily precipitate in the resultantcoating liquid.

[0241] When alumina is used as a dispersing medium, the abrasion amountof alumina is much less than zirconia, and therefore the influence onresidual potential is very little. Therefore alumina is preferable asthe dispersing medium. In addition, it is preferable to use alumina as afiller when alumina balls are used as the dispersing medium.

[0242] When the protective layer coating liquid is prepared, the organiccompound having such a specific acid value is preferably mixed with afiller and an organic solvent before the dispersion process. In thiscase, agglomeration and precipitation of the filler in the coatingliquid can be prevented and the dispersibility of the filler can bedramatically improved. A binder resin, and a CTM can be mixed with thematerials before the dispersion process, but there is a case where thedispersibility of the filler slightly deteriorates. Therefore, it ispreferable to add a binder resin and a CTM, which are dissolved in anorganic solvent.

[0243] When the protective layer is formed, a known coating method suchas dip coating methods, spray coating methods, bead coating methods,nozzle coating methods and ring coating methods can be used. Inparticular, spray coating methods are preferably used to prepare auniform film. The protective layer can be formed by performing coatingonce or more times. However, it is preferable to perform coating twiceor more times (i.e., to form a multi-layered protective layer), becausethe filler is uniformly dispersed in the resultant layer withoutagglomerating. By forming the protective layer by this method, theresultant photoreceptor has good abrasion resistance and can produceimages having good resolution without causing the residual potentialincreasing problem.

[0244] The thickness of the protective layer is preferably from 0.1 to10 μm. By including an organic compound having an acid value of from 10to 700 mgKOH/g therein, the residual potential can be dramaticallydecreased, and thereby the flexibility in designing the thickness of theprotective layer can be improved. However, the protective layer is toothick, the image qualities slightly deteriorates, and therefore it isnot preferable.

[0245] In the photoreceptor of the present invention, an intermediatelayer can be formed between the protective layer and the photosensitivelayer (i.e., between the protective layer 39 and the single-layeredphotosensitive layer 33 in FIG. 3, the CTL 37 in FIG. 4 or the CGL 35 inFIG. 5). The intermediate layer includes a binder resin as a maincomponent. Specific examples of the resins include polyamide resins,alcohol-soluble nylon, water-soluble polyvinyl butyral, polyvinylbutyral, polyvinyl alcohol, etc. The intermediate layer can be formed bysuch a known coating method as mentioned above. The thickness of theintermediate layer is from 0.05 to 2 μm.

[0246] In the photoreceptor of the present invention, one or moreadditives such as antioxidants, plasticizers, lubricants, ultravioletabsorbents, low molecular weight charge transport materials and levelingagents can be used in one or more layers of the CGL, CTL, undercoatlayer, protective layer and intermediate layers to improve the stabilityto withstand environmental conditions, namely to avoid decrease ofphotosensitivity and increase of residual potential.

[0247] Suitable antioxidants for use in the layers of the photoreceptorinclude the following compounds but are not limited thereto.

[0248] (a) Phenolic Compounds

[0249] 2,6-di-t-butyl-p-cresol, butylated hydroxyanisole,2,6-di-t-butyl-4-ethylphenol,n-octadecyl-3-(4′-hydroxy-3′,5′-di-t-butylphenol),2,2′-methylene-bis-(4-methyl-6-t-butylphenol),2,2′-methylene-bis-(4-ethyl-6-t-butylphenol),4,4′-thiobis-(3-methyl-6-t-butylphenol),4,4′-butylidenebis-(3-methyl-6-t-butylphenol),1,1,3-tris-(2-methyl-4-hydroxy-5-t-butylphenyl)butane,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane,bis[3,3′-bis(4′-hydroxy-3′-t-butylphenyl)butyric acid]glycol ester,tocophenol compounds, and the like.

[0250] (b) Paraphenylenediamine Compounds

[0251] N-phenyl-N′-isopropyl-p-phenylenediamine,N,N′-di-sec-butyl-p-phenylenediamine,N-phenyl-N-sec-butyl-p-phenylenediamine,N,N′-di-isopropyl-p-phenylenediamine,N,N′-dimethyl-N,N′-di-t-butyl-p-phenylenediamine, and the like.

[0252] (c) Hydroquinone Compounds

[0253] 2,5-di-t-octylhydroquinone, 2,6-didodecylhydroquinone,2-dodecylhydroquinone, 2-dodecyl-5-chlorohydroquinone,2-t-octyl-5-methylhydroquinone, 2-(2-octadecenyl)-5-methylhydroquinoneand the like.

[0254] (d) Organic Sulfur-Containing Compounds

[0255] dilauryl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate,ditetradecyl-3,3′-thiodipropionate, and the like.

[0256] (e) Organic Phosphorus-Containing Compounds

[0257] triphenylphosphine, tri(nonylphenyl)phosphine,tri(dinonylphenyl)phosphine, tricresylphosphine,tri(2,4-dibutylphenoxy)phosphine and the like.

[0258] Suitable plasticizers for use in the layers of the photoreceptorinclude the following compounds but are not limited thereto:

[0259] (a) Phosphoric Acid Esters

[0260] triphenyl phosphate, tricresyl phosphate, trioctyl phosphate,octyldiphenyl phosphate, trichloroethyl phosphate, cresyldiphenylphosphate, tributyl phosphate, tri-2-ethylhexyl phosphate, triphenylphosphate, and the like.

[0261] (b) Phthalic Acid Esters

[0262] dimethyl phthalate, diethyl phthalate, diisobutyl phthalate,dibutyl phthalate, diheptyl phthalate, di-2-ethylhexyl phthalate,diisooctyl phthalate, di-n-octyl phthalate, dinonyl phthalate,diisononyl phthalate, diisodecyl phthalate, diundecyl phthalate,ditridecyl phthalate, dicyclohexyl phthalate, butylbenzyl phthalate,butyllauryl phthalate, methyloleyl phthalate, octyldecyl phthalate,dibutyl fumarate, dioctyl fumarate, and the like.

[0263] (c) Aromatic Carboxylic Acid Esters

[0264] trioctyl trimellitate, tri-n-octyl trimellitate, octyloxybenzoate, and the like.

[0265] (d) Dibasic Fatty Acid Esters

[0266] dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate,di-n-octyl adipate, n-octyl-n-decyl adipate, diisodecyl adipate, dialkyladipate, dicapryl adipate, di-2-etylhexyl azelate, dimethyl sebacate,diethyl sebacate, dibutyl sebacate, di-n-octyl sebacate, di-2-ethylhexylsebacate, di-2-ethoxyethyl sebacate, dioctyl succinate, diisodecylsuccinate, dioctyl tetrahydrophthalate, di-n-octyl tetrahydrophthalate,and the like.

[0267] (e) Fatty Acid Ester Derivatives

[0268] butyl oleate, glycerin monooleate, methyl acetylricinolate,pentaerythritol esters, dipentaerythritol hexaesters, triacetin,tributyrin, and the like.

[0269] (f) Oxyacid Esters

[0270] methyl acetylricinolate, butyl acetylricinolate,butylphthalylbutyl glycolate, tributyl acetylcitrate, and the like.

[0271] (g) Epoxy Compounds

[0272] epoxydized soybean oil, epoxydized linseed oil, butylepoxystearate, decyl epoxystearate, octyl epoxystearate, benzylepoxystearate, dioctyl epoxyhexahydrophthalate, didecylepoxyhexahydrophthalate, and the like.

[0273] (h) Dihydric Alcohol Esters diethylene glycol dibenzoate,triethylene glycol di-2-ethylbutyrate, and the like.

[0274] (i) Chlorine-Containing Compounds

[0275] chlorinated paraffin, chlorinated diphenyl, methyl esters ofchlorinated fatty acids, methyl esters of methoxychlorinated fattyacids, and the like.

[0276] (j) Polyester Compounds

[0277] polypropylene adipate, polypropylene sebacate, acetylatedpolyesters, and the like.

[0278] (k) Sulfonic Acid Derivatives

[0279] p-toluene sulfonamide, o-toluene sulfonamide, p-toluenesulfoneethylamide, o-toluene sulfoneethylamide, toluenesulfone-N-ethylamide, p-toluene sulfone-N-cyclohexylamide, and the like.

[0280] (1) Citric Acid Derivatives

[0281] triethyl citrate, triethyl acetylcitrate, tributyl citrate,tributyl acetylcitrate, tri-2-ethylhexyl acetylcitrate, n-octyldecylacetylcitrate, and the like.

[0282] (m) Other Compounds

[0283] terphenyl, partially hydrated terphenyl, camphor, 2-nitrodiphenyl, dinonyl naphthalene, methyl abietate, and the like.

[0284] Suitable lubricants for use in the layers of the photoreceptorinclude the following compounds but are not limited thereto.

[0285] (a) Hydrocarbons

[0286] liquid paraffins, paraffin waxes, micro waxes, low molecularweight polyethylenes, and the like.

[0287] (b) Fatty Acids

[0288] lauric acid, myristic acid, palmitic acid, stearic acid,arachidic acid, behenic acid, and the like.

[0289] (c) Fatty Acid Amides

[0290] Stearic acid amide, palmitic acid amide, oleic acid amide,methylenebisstearamide, ethylenebisstearamide, and the like.

[0291] (d) Ester Compounds

[0292] lower alcohol esters of fatty acids, polyhydric alcohol esters offatty acids, polyglycol esters of fatty acids, and the like.

[0293] (e) Alcohols

[0294] cetyl alcohol, stearyl alcohol, ethylene glycol, polyethyleneglycol, polyglycerol, and the like.

[0295] (f) Metallic Soaps

[0296] lead stearate, cadmium stearate, barium stearate, calciumstearate, zinc stearate, magnesium stearate, and the like.

[0297] (g) Natural Waxes

[0298] Carnauba wax, candelilla wax, beeswax, spermaceti, insect wax,montan wax, and the like.

[0299] (h) Other Compounds

[0300] silicone compounds, fluorine compounds, and the like.

[0301] Suitable ultraviolet absorbing agents for use in the layers ofthe photoreceptor include the following compounds but are not limitedthereto.

[0302] (a) Benzophenone Compounds

[0303] 2-hydroxybenzophenone, 2,4-dihydroxybenzophenone,2,2′,4-trihydroxybenzophenone, 2,2′,4,4′-tetrahydroxybenzophenone,2,2′-dihydroxy-4-methoxybenzophenone, and the like.

[0304] (b) Salicylate Compounds

[0305] phenyl salicylate,2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate, and the like.

[0306] (c) Benzotriazole Compounds

[0307] (2′-hydroxyphenyl)benzotriazole,(2′-hydroxy-5′-methylphenyl)benzotriazole,(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole, and thelike.

[0308] (d) Cyano Acrylate Compounds

[0309] ethyl-2-cyano-3,3-diphenyl acrylate,methyl-2-carbomethoxy-3-(paramethoxy) acrylate, and the like.

[0310] (e) Quenchers (Metal Complexes)

[0311] nickel(2,2′-thiobis(4-t-octyl)phenolate)-n-butylamine,nickeldibutyldithiocarbamate, cobaltdicyclohexyldithiophosphate, and thelike.

[0312] (f) HALS (Hindered Amines)

[0313] bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate,bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate,1-[2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}ethyl]-4-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}-2,2,6,6-tetrametylpyridine,8-benzyl-7,7,9,9-tetramethyl-3-octyl-1,3,8-triazaspiro[4,5]undecane-2,4-dione,4-benzoyloxy-2,2,6,6-tetramethylpiperidine, and the like.

[0314] Hereinafter electrophotographic image forming method andapparatus will be explained as embodiments of the image forming methodand image forming apparatus of the present invention referring todrawings. However, the image forming method and image forming apparatusof the present invention are not limited thereto.

[0315]FIG. 6 is a schematic view for explaining electrophotographicimage forming method and apparatus according to an embodiment of thepresent invention.

[0316] In FIG. 6, numeral 1 denotes a photoreceptor. The photoreceptor 1is the photoreceptor of the present invention which includes at least aphotosensitive layer located overlying an electroconductive substrate,wherein the photoreceptor is the photoreceptor of the present invention.The photoreceptor 1 has a drum form, but sheet-form and endlessbelt-form photoreceptors can also be used.

[0317] Around the photoreceptor 1, a discharging lamp 2, a charger 3configured to charge the photoreceptor 1, an imagewise light irradiator5 configured to irradiate the photoreceptor 1 with imagewise light toform an electrostatic latent image on the photoreceptor 1, an imagedeveloper 6 configured to develop the latent image with a toner to forma toner image on the photoreceptor 1, a cleaning unit including acleaning brush 14 and a cleaning blade 15 configured to clean thesurface of the photoreceptor 1 are arranged while contacting or beingset closely to the photoreceptor 1. The toner image formed on thephotoreceptor 1 is transferred on a receiving paper 9 fed by a pair ofregistration rollers 8 at the transfer device (i.e., a pair of atransfer charger 10 and a separating charger 11). The receiving paper 9having the toner image thereon is separated from the photoreceptor 1 bya separating pick 12.

[0318] In the image forming apparatus of the present invention, apre-transfer charger 7 and a pre-cleaning charger 13 may be arranged ifdesired.

[0319] As the charger 3, the pre-transfer charger 7, the transfercharger 10, the separating charger 11 and the pre-cleaning charger 13,all known chargers such as corotrons, scorotrons, solid state chargers,roller chargers and brush chargers can be used.

[0320] As the transfer device, the above-mentioned chargers can be used.Among the chargers, a combination of the transfer charger 10 and theseparating charger 11 as shown in FIG. 6 is preferably used.

[0321] Suitable light sources for use in the imagewise light irradiator5 and the discharging lamp 2 include fluorescent lamps, tungsten lamps,halogen lamps, mercury lamps, sodium lamps, light emitting diodes(LEDs), laser diodes (LDs), light sources using electroluminescence(EL), and the like. In addition, in order to obtain light having adesired wave length range, filters such as sharp-cut filters, band passfilters, near-infrared cutting filters, dichroic filters, interferencefilters, color temperature converting filters and the like can be used.

[0322] The above-mentioned lamps can be used for not only the processesmentioned above and illustrated in FIG. 6, but also other processesusing light irradiation, such as a transfer process including lightirradiation, a discharging process, a cleaning process including lightirradiation and a pre-exposure process.

[0323] When the toner image formed on the photoreceptor 1 by thedeveloping unit 6 is transferred onto the receiving paper 9, all of thetoner image are not transferred on the receiving paper 9, and residualtoner particles remain on the surface of the photoreceptor 1. Theresidual toner is removed from the photoreceptor 1 by the fur blush 14or the cleaning blade 15. The residual toner remaining on thephotoreceptor 1 can be removed by only a cleaning brush. Suitablecleaning blushes include known cleaning blushes such as fur blushes andmag-fur blushes.

[0324] When the photoreceptor 1 which is previously charged positively(or negatively) is exposed to imagewise light, an electrostatic latentimage having a positive or negative charge is formed on thephotoreceptor 1. When the latent image having a positive (or negative)charge is developed with a toner having a negative (or positive) charge,a positive image can be obtained. In contrast, when the latent imagehaving a positive (negative) charge is developed with a toner having apositive (negative) charge, a negative image (i.e., a reversal image)can be obtained. As the developing method, known developing methods canbe used. In addition, as the discharging methods, known dischargingmethods can also be used.

[0325]FIG. 7 is a schematic view illustrating another embodiment of theelectrophotographic image forming apparatus according to the presentinvention. In this embodiment, a belt-shaped photoreceptor 21 is used.The photoreceptor 21 is the photoreceptor of the present invention.

[0326] The belt-shaped photoreceptor 21 is rotated by rollers 22 a and22 b. The photoreceptor 21 is charged with a charger 23, and thenexposed to imagewise light emitted by an imagewise light irradiator 24to form an electrostatic latent image on the photoreceptor 21. Thelatent image is developed with a developing unit 29 to form a tonerimage on the photoreceptor 21. The toner image is transferred onto areceiving paper (not shown) using a transfer charger 25. After the tonerimage transferring process, the surface of the photoreceptor 21 iscleaned with a cleaning brush 27 after performing a pre-cleaning lightirradiating operation using a pre-cleaning light irradiator 26. Then thephotoreceptor 21 is discharged by being exposed to light emitted by adischarging light source 28. In the pre-cleaning light irradiatingprocess, light irradiates the photoreceptor 21 from the side of thesubstrate thereof. In this case, the substrate has to belight-transmissive.

[0327] The image forming apparatus of the present invention is notlimited to the image forming units as shown in FIGS. 6 and 7. Forexample, in FIG. 7, the pre-cleaning light irradiating operation can beperformed from the photosensitive layer side of the photoreceptor 21. Inaddition, the light irradiation in the light image irradiating processand the discharging process may be performed from the substrate side ofthe photoreceptor 21.

[0328] Further, a pre-transfer light irradiation operation, which isperformed before the transferring of the toner image, and a preliminarylight irradiation operation, which is performed before the imagewiselight irradiation, and other light irradiation operations may also beperformed.

[0329] The above-mentioned image forming unit may be fixedly set in acopier, a facsimile or a printer. However, the image forming unit may beset therein as a process cartridge. The process cartridge means an imageforming unit which includes a photoreceptor and at least one or more ofa charger, an imagewise light irradiator, an image developer, an imagetransfer device, a cleaner, and a discharger.

[0330]FIG. 8 is a schematic view illustrating an embodiment of theprocess cartridge of the present invention. In FIG. 8, the processcartridge includes a photoreceptor 16, a charger 17 configured to chargethe photoreceptor 16, a cleaning brush 18 configured to clean thesurface of the photoreceptor 16, an imagewise light irradiator 19configured to irradiate the photoreceptor 16 with imagewise light toform an electrostatic latent image on the photoreceptor 16, and an imagedeveloper (a developing roller) 20 configured to develop the latentimage with a toner. The photoreceptor 16 is the photoreceptor of thepresent invention. The process cartridge of the present invention is notlimited thereto.

[0331] Having generally described this invention, further understandingcan be obtained by reference to certain specific examples which areprovided herein for the purpose of illustration only and are notintended to be limiting. In the descriptions in the following examples,the numbers represent weight ratios in parts, unless otherwisespecified.

EXAMPLES Example 1

[0332] Each of the following undercoat layer coating liquid, CGL coatingliquid and CTL coating liquid was coated on an aluminum cylinder by dipcoating followed by drying one by one to overlay an undercoat layerhaving a thickness of 3.5 μm, a CGL having a thickness of 0.2 μm, andCTL having a thickness of 23 μm. Undercoat Layer coating liquid Titaniumdioxide 400 parts Melamine resin 65 parts Alkyd resin 120 parts2-butanone 400 parts CGL coating liquid Polyvinyl butyral 5 parts Bisazopigment having the following formula (16) 12 parts (16)

2-butanone 200 parts Cyclohexanone 400 parts CTL coating liquidPolycarbonate 10 parts (Z-form polycarbonate from Teijin Chemical Co.,Ltd.) 10 parts CTM having the following formula (17) (17)

Tetrahydrofuran 100 parts

[0333] Then the following protective layer coating liquid was coated onthe CTL by spray coating, followed by drying to form a protective layerhaving a thickness of about 4 μm. Protective layer coating liquidα-alumina 2 parts (SUMICORUNDUM AA-03 from Sumitomo Chemical Co., Ltd.,average primary particular diameter of 0.3 μm, resistivity of not lessthan 10¹⁰ Ω · cm, and pH of from 8 to 9) Compound No. 4 illustrated inTable 1 0.5 parts Solution of unsaturated 0.02 parts polycarboxylic acidpolymer (BYK-P104 from BYK Chemie, acid value of about 180 mgKOH/g, andsolid content of 50%) CTM having formula (17) 3.5 parts Polycarbonateresin 6 parts (Z-form polycarbonate resin from Teijin Chemical Co.,Ltd.) Tetrahydrofuran 220 parts Cyclohexanone 80 parts

Example 2

[0334] The procedure for preparation of the photoreceptor in Example 1was repeated except that the polycarboxylic acid polymer in theprotective layer was replaced with 0.02 parts of an unsaturatedpolycarboxylic acid polymer (BYK-PIOS from BYK Chemie, acid value of 365mgKOH/g).

[0335] Thus, a photoreceptor of Example 2 was prepared.

Example 3

[0336] The procedure for preparation of the photoreceptor in Example 1was repeated except that the polycarboxylic acid polymer in theprotective layer was replaced with 0.2 parts of a polyester resin havingan acid value of 35 mgKOH/g.

[0337] Thus, a photoreceptor of Example 3 was prepared.

Example 4

[0338] The procedure for preparation of the photoreceptor in Example 1was repeated except that the polycarboxylic acid polymer in theprotective layer was replaced with 0.2 parts of a polyester resin havingan acid value of 50 mgKOH/g.

[0339] Thus, a photoreceptor of Example 4 was prepared.

Example 5

[0340] The procedure for preparation of the photoreceptor in Example 1was repeated except that the polycarboxylic acid polymer in theprotective layer was replaced with 0.1 parts of an acrylic resin (DIANALBR-605 from Mitsubishi Rayon Co., Ltd., acid value of 65 mgKOH/g).

[0341] Thus, a photoreceptor of Example 5 was prepared.

Example 6

[0342] The procedure for preparation of the photoreceptor in Example 1was repeated except that the polycarboxylic acid polymer in theprotective layer was replaced with 0.1 parts of a copolymer of acrylicacid and hydroxyethyl methacrylate having an acid value of 50 mgKOH/g.

[0343] Thus, a photoreceptor of Example 6 was prepared.

Example 7

[0344] The procedure for preparation of the photoreceptor in Example 1was repeated except that the polycarboxylic acid polymer in theprotective layer was replaced with 0.1 parts of a copolymer of monoesterof maleic acid, styrene and butyl acrylate having an acid value of 50mgKOH/g.

[0345] Thus, a photoreceptor of Example 7 was prepared.

Example 8

[0346] The procedure for preparation of the photoreceptor in Example 1was repeated except that the polycarboxylic acid polymer in theprotective layer was replaced with 0.1 parts of a styrene-acryliccopolymer (FB-1522 from Mitsubishi Rayon Co., Ltd., acid value of 200mgKOH/g).

[0347] Thus, a photoreceptor of Example 8 was prepared.

Example 9

[0348] The procedure for preparation of the photoreceptor in Example 1was repeated except that the polycarboxylic acid polymer in theprotective layer was replaced with 0.02 parts of a solution of anunsaturated polycarboxylic acid polymer (from Fujisawa PharmaceuticalCo., Ltd., acid value of 650 mgKOH/g).

[0349] Thus, a photoreceptor of Example 9 was prepared.

Example 10

[0350] The procedure for preparation of the photoreceptor in Example 2was repeated except that the addition amount of the unsaturatedpolycarboxylic acid polymer solution was changed to 0.001 parts.

[0351] Thus, a photoreceptor of Example 10 was prepared.

Example 11

[0352] The procedure for preparation of the photoreceptor in Example 2was repeated except that the addition amount of the unsaturatedpolycarboxylic acid polymer solution was changed to 0.1 parts.

[0353] Thus, a photoreceptor of Example 11 was prepared.

Example 12

[0354] The procedure for preparation of the photoreceptor in Example 5was repeated except that the addition amount of the acrylic resin waschanged to 0.5 parts.

[0355] Thus, a photoreceptor of Example 12 was prepared.

Example 13

[0356] The procedure for preparation of the photoreceptor in Example 1was repeated except that the filler (i.e., alumina) included in theprotective layer was replaced with 2 parts of a titanium oxide having anaverage primary particle diameter of 0.3 μm (CR-97 from Ishihara SangyoKaisha Ltd.).

[0357] Thus, a photoreceptor of Example 13 was prepared.

Example 14

[0358] The procedure for preparation of the photoreceptor in Example 1was repeated except that the filler included in the protective layer wasreplaced with 2 parts of a titanium oxide having an average primaryparticle diameter of 0.015 μm and treated with a silane coupling agent(MT10OSA from Tayca Corp., ratio of titanium oxide to silane couplingagent 100/20).

[0359] Thus, a photoreceptor of Example 14 was prepared.

Example 15

[0360] The procedure for preparation of the photoreceptor in Example 1was repeated except that the filler included in the protective layer wasreplaced with 2 parts of a silica having an average particle diameter of0.1 μm (KMPX100 from Shin-Etsu Chemical Co., Ltd.).

[0361] Thus, a photoreceptor of Example 15 was prepared.

Example 16

[0362] The procedure for preparation of the photoreceptor in Example 1was repeated except that the binder resin and the CTM included in theprotective layer were replaced with 20 parts of a charge transportpolymer having the following formula (18).

[0363] Thus, a photoreceptor of Example 16 was prepared.

Example 17

[0364] The procedure for preparation of the photoreceptor in Example 1was repeated except that the binder resin (i.e., polycarbonate) includedin the protective layer was replaced with 10 parts of a polyarylateresin (U POLYMER from Unitika Ltd.)

[0365] Thus, a photoreceptor of Example 17 was prepared.

Example 18

[0366] The procedure for preparation of the photoreceptor in Example 1was repeated except that the CGL coating liquid, the CTL coating liquidand the protective layer coating liquid were changed to the following.CGL coating liquid Titanyl phthalocyanine having an X-ray diffraction 8parts spectrum illustrated in FIG. 9 Polyvinyl butyral 5 parts2-butanone 400 parts CTL coating liquid C-form polycarbonate resin 10parts CTM having the following formula (19) 8 parts (19)

Toluene 70 parts Protective layer coating liquid Titanium oxide treatedwith alumina 1.5 parts (from Tayca, an average primary particle diameterof 0.035 μm) Compound No. 4 illustrated in Table 1 0.5 parts Methacrylicacid/methyl methacrylate copolymer 0.5 parts (acid value of 50 mgKOH/g)4 parts CTM having formula (19) Tetrahydrofuran 250 parts Cyclohexanone50 parts Thus, a photoreceptor of Example 18 was prepared.

Comparative Example 1

[0367] The procedure for preparation of the photoreceptor in Example 1was repeated except that the protective layer coating liquid werechanged to the following. Protective layer coating liquid Alumina 2parts (SUMICORUNDUM AA-03 from Sumitomo Chemical Co., Ltd., averageprimary particular diameter of 0.3 μm) Compound No. 4 illustrated inTable 1 0.5 parts CTM having formula (17) 4 parts Z-form polycarbonate 6parts (from Teijin Chemicals Ltd.) Tetrahydrofuran 220 partsCyclohexanone 80 parts

Comparative Example 2

[0368] The procedure for preparation of the photoreceptor in Example 3was repeated except that the protective layer coating liquid werechanged to the following. Protective layer coating liquid Alumina 2parts (SUMICORUNDUM AA-03 from Sumitomo Chemical Co., Ltd., averageprimary particular diameter of 0.3 μm) Compound No. 4 listed in Table 10.5 parts Polyester resin 0.2 parts (acid value of 7 mgKOH/g) CTM havingformula (17) 4 parts Z-form polycarbonate 6 parts (from Teijin ChemicalsLtd.) Tetrahydrofuran 220 parts Cyclohexanone 80 parts

Comparative Example 3

[0369] The procedure for preparation of the photoreceptor in Example 1was repeated except that the protective layer coating liquid werechanged to the following. Protective layer coating liquid Alumina 2parts (SUMICORUNDUM AA-03 from Sumitomo Chemical Co., Ltd., averageprimary particular diameter of 0.3 μm) Unsaturated polycarboxylic 0.02parts acid polymer solution (from BYK Chemie, acid value of 180 mgKOH/g)CTM having formula (17) 4 parts Z-form polycarbonate 6 parts (fromTeijin Chemicals Ltd.) Tetrahydrofuran 220 parts Cyclohexanone 80 parts

Example 19

[0370] The procedure for preparation of the photoreceptor in Example 1was repeated except that the compound No. 4 in the protective layercoating liquid was replaced with a compound No. 2 illustrated in Table1.

[0371] Thus, a photoreceptor of Example 19 was prepared.

Example 20

[0372] The procedure for preparation of the photoreceptor in Example 1was repeated except that the compound No. 4 in the protective layercoating liquid was replaced with a compound No. 17 illustrated in Table2.

[0373] Thus, a photoreceptor of Example 20 was prepared.

Example 21

[0374] The procedure for preparation of the photoreceptor in Example 1was repeated except that the compound No. 4 in the protective layercoating liquid was replaced with a compound No. 20 illustrated in Table2.

[0375] Thus, a photoreceptor of Example 21 was prepared.

Example 22

[0376] The procedure for preparation of the photoreceptor in Example 1was repeated except that the compound No. 4 in the protective layercoating liquid was replaced with a compound No. 23 illustrated in Table2.

[0377] Thus, a photoreceptor of Example 22 was prepared.

Example 23

[0378] The procedure for preparation of the photoreceptor in Example 1was repeated except that the compound No. 4 in the protective layercoating liquid was replaced with a compound No. 30 illustrated in Table3.

[0379] Thus, a photoreceptor of Example 23 was prepared.

[0380] Evaluation Method

[0381] Each of the photoreceptors of Examples 1 to 23 and ComparativeExamples 1 to 3 was set in a process cartridge, and the cartridge wasset in an image forming apparatus, IMAGIO MF2200 manufactured by RicohCo., Ltd., which had been modified such that a scorotron corona chargeris used as the charger; and a laser diode emitting light having awavelength of 655 nm is used as a light source for the imagewise lightirradiator. The potential of non-lighted portions of each photoreceptorwas controlled so as to be −900 V. A running test in which 50,000 imageswere continuously produced was performed to evaluate the image qualitiesof images produced at the beginning and end of the running test. Inaddition, the potential (PL) of lighted portions (i.e., the residualpotential) of each photoreceptor was measured at the beginning and endof the running test. Further, the difference-in thickness of theprotective layer before and after the running test was determined todetermine the abrasion amount of the protective layer.

[0382] The results are shown in Table 4. TABLE 4 At the beginning ofrunning test At the end of running test P_(L) Image P_(L) Image Abrasion(−V) qualities (−V) qualities (μM) Ex. 1 115 Good 160 good 0.50 Ex. 2110 Good 150 good 0.51 Ex. 3 160 Good 225 good 0.52 Ex. 4 140 Good 220good 0.52 Ex. 5 145 Good 205 good 0.51 Ex. 6 120 Good 200 good 0.51 Ex.7 120 Good 180 good 0.50 Ex. 8 130 Good 180 good 0.56 Ex. 9 110 Good 155good 0.54 Ex. 10 205 Good 300 Low image 0.55 density Ex. 11 105 Good 150good 0.52 Ex. 12 125 Good 200 good 0.51 Ex. 13 140 Good 195 good 0.55Ex. 14 130 Good 180 good 0.72 Ex. 15 120 Good 175 good 0.80 Ex. 16 120Good 180 good 0.49 Ex. 17 140 Good 190 good 0.52 Ex. 18 135 Good 200good 0.47 Comp. 270 Slightly low 400 Very low image 1.02 Ex. 1 imagedensity density. Image cannot be read. Comp. 250 Low image 365 Very lowimage 0.96 Ex. 2 density density. Image cannot be read. Comp. 125 Good160 Very low image 0.52 Ex. 3 density. Ex. 19 120 Good 160 good 0.51 Ex.20 125 Good 165 good 0.52 Ex. 21 115 Good 165 good 0.50 Ex. 22 115 Good155 good 0.51 Ex. 23 120 Good 160 good 0.53

[0383] As clearly understood from the data as shown in-Table 4, thepotential (P_(L)) of lighted potions (i.e., the residual potential) ofthe photoreceptors of the present invention is relatively low comparedto that of comparative photoreceptors. This is because an organiccompound having an acid value of from 10 to 700 mgKOH/g is included inthe outermost layer. In addition, it is clear that when a compoundhaving formula (1) is added to the outermost layer, the resultantphotoreceptors can produce high quality images for a long period of timewhile the outermost layer is hardly abraded.

[0384] In contrast, the photoreceptors, which include no organiccompound having an acid value of from 10 to 700 mgKOH/g or include acompound having an acid value less than 10 mgKOH/g, have very highresidual potential even at the beginning of the running test, andthereby the resultant images have low image density and poor resolution.In addition, at the end of the running test, the half tonereproducibility of the images seriously deteriorates, and thereby theimages cannot be read. Further, the photoreceptors have poor abrasionresistance.

[0385] In addition, images were produced using the photoreceptors ofExamples 1, 11, and 19 to 23 and Comparative Example 3 were allowed tosettle in a desiccator containing air including NOx gasses at aconcentration of 50 ppm for four days, to compare the resolution of theimages with that of the initial images of the respective photoreceptors.

[0386] The results are shown in Table 5. TABLE 5 Resolution Resolutionof of initial images after images (lines/mm) the test (lines/mm) Ex. 18.0 8.0 Ex. 11 8.0 7.2 Comp. Ex. 3 8.0 2.8 Ex. 19 8.0 8.0 Ex. 20 8.0 8.0Ex. 21 8.0 8.0 Ex. 22 8.0 8.0 Ex. 23 8.0 8.0

[0387] As clearly understood from the data as shown in Table 5, thephotoreceptors including a compound having formula (1) have excellentresistance to NOx gasses. The images produced by the photoreceptor ofExample 11, which has relatively large acid equivalent compared to thephotoreceptors of Examples 1, and 19 to 23, have relatively lowresolution, although the image qualities are still acceptable.

Example 24

[0388] The following protective layer coating liquid B was prepared.Protective layer coating liquid Alumina 2 parts (SUMICORUNDUM AA-03 fromSumitomo Chemical Co., Ltd., average primary particular diameter of 0.3μm) Compound No.2 illustrated in Table 1 0.5 parts Unsaturatedpolycarboxylic acid polymer solution 0.02 parts (from BYK Chemie, acidvalue of 180 mgKOH/g) CTM having formula (17) 3.5 parts Z-formpolycarbonate 6 parts (from Teijin Chemicals Ltd.) 0.005 partsHydroquinone compound having the following formula (20) (20)

Tetrahydrofuran 220 parts Cyclohexanone 80 parts

Example 25

[0389] The procedure for preparation of the protective layer coatingliquid in Example 24 was repeated except that the hydroquinone compoundhaving formula (20) was replaced with a hindered amine compound havingthe following formula (21).

[0390] Thus, a protective layer coating liquid C was prepared.

Example 26

[0391] The procedure for preparation of the protective layer coatingliquid in Example 24 was repeated except that the hydroquinone compoundhaving formula (20) was replaced with an organic sulfur-containingcompound having the following formula (22).

[0392] Thus, a protective layer coating liquid D was prepared.

Example 27

[0393] The procedure for preparation of the protective layer coatingliquid in Example 24 was repeated except that the hydroquinone compoundhaving formula (20) was replaced with a hindered phenol compound havingthe following formula (23).

[0394] Thus, a protective layer coating liquid E was prepared.

Example 28

[0395] The procedure for preparation of the protective layer coatingliquid in Example 24 was repeated except that the hydroquinone compoundhaving formula (20) was replaced with an organic phosphorous-containingcompound having the following formula (24).

[0396] Thus, a protective layer coating liquid F was prepared.

[0397] The thus prepared protective layer coating liquids B to F and theprotective layer coating liquid (i.e., protective layer coating liquidA) prepared in Examples 1 were allowed to settle in a dark place at roomtemperature to determine whether the spectral absorption property ofeach coating liquid changes after the preservation test.

[0398] The results are shown in Table 6 TABLE 6 Protective layer Rate*of change coating liquid in absorption at 665 nm A 1.17 B 1.01 C 1.01 D1.07 E 1.09 F 1.10

[0399] As clearly understood from the data as shown in Table 6, additionof an antioxidant in the protective layer coating liquid improves thepreservability of the protective layer coating liquid. In particular,the hydroquinone compound and hindered amine compound have goodimproving effect.

Example 29

[0400] Each of the following undercoat layer coating liquid, a CGLcoating liquid and a CTL coating liquid was coated on an aluminumcylinder by dip coating followed by drying one by one to overlay anundercoat layer having a thickness of 3.5 μm, a CGL having a thicknessof 0.2 μm, and CTL having a thickness of 23 μm. Undercoat layer coatingliquid Titanium dioxide 400 parts Melamine resin 65 parts Alkyd resin120 parts 2-butanone 400 parts CGL coating liquid Polyvinyl butyral 5parts Bisazo pigment having the following formula (16) 12 parts (25)

2-butanone 200 parts Cyclohexanone 400 parts CTL coating liquidPolycarbonate 10 parts (Z-form polycarbonate from Teijin Chemical Co.,Ltd.) 10 parts Compound No. 1 illustrated in Table 1 Tetrahydrofuran 100parts Thus, a photoreceptor of Example 24 was prepared.

Examples 30 to 43

[0401] The procedure for preparation of the photoreceptor in Example 29was repeated except that the compound No. 1 was replaced with a compoundas listed in Table 7.

[0402] Thus, photoreceptors of Examples 30 to 43 were prepared.

[0403] Evaluation Method

[0404] Each of the thus prepared photoreceptors of Examples 29 to 43 wasset in a process cartridge, and the cartridge was set in an imageforming apparatus, IMAGIO MF2200 manufactured by Ricoh Co., Ltd., whichhad been modified such that a scorotron corona charger is used as thecharger; and a laser diode emitting light having a wavelength of 655 nmis used as a light source for the imagewise light irradiator. Thepotential of non-lighted portions of each photoreceptor was controlledso as to be −800 V. A running test in which 100,000 images werecontinuously produced was performed to evaluate the image qualities ofimages produced at the beginning and end of the running test. Inaddition, the potential (P_(L)) of lighted portions (i.e., the residualpotential) of each photoreceptor was measured at the beginning and endof the running test. Further, the difference in thickness of theprotective layer before and after the running test was determined todetermine the abrasion amount of the protective layer.

[0405] The results are shown in Table 7. TABLE 7 At the beginning of Atthe end of the running test the running test Compound P_(L) Image P_(L)No. (−V) qualities (−V) Image qualities Ex. 29 1 105 Good 125 good Ex.30 2 110 Good 135 good Ex. 31 3 100 Good 140 good Ex. 32 4 95 Good 120good Ex. 33 6 95 Good 125 Slightly low image density Ex. 34 11 105 Good135 good Ex. 35 14 105 Good 130 good Ex. 36 16 125 Good 155 Slightly lowimage density Ex. 37 17 100 Good 120 good Ex. 38 21 120 Good 155Slightly low image density Ex. 39 23 100 Good 165 Slightly low imagedensity Ex. 40 26 115 Good 140 good Ex. 41 29 105 Good 160 Slightly lowimage density Ex. 42 31 120 Good 130 good Ex. 43 35 100 Good 135 good

Examples 44

[0406] The procedure for preparation and evaluation of the photoreceptorin Example 29 was repeated except that the CTL coating liquid wasreplaced with the following. CTL coating liquid Polycarbonate 10 parts(Z-form polycarbonate from Teijin Chemical Co., Ltd.) Compound No. 1illustrated in Table 1 1 part CTM having formula (17) 9 partsTetrahydrofuran 100 parts

Examples 45 to 58

[0407] The procedure for preparation of the photoreceptor in Example 44was repeated except that the compound No. 1 was replaced with a compoundas listed in Table 8.

[0408] The evaluation results are shown in Table 8. TABLE 8 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 44 1 95Good 105 good Ex. 45 2 100 Good 110 good Ex. 46 3 100 Good 105 good Ex.47 4 95 Good 105 good Ex. 48 6 100 Good 110 good Ex. 49 11 100 Good 110good Ex. 50 14 100 Good 115 good Ex. 51 16 100 Good 105 good Ex. 52 17100 Good 110 good Ex. 53 21 105 Good 110 good Ex. 54 23 100 Good 105good Ex. 55 26 115 Good 105 good Ex. 56 29 100 Good 115 good

Examples 59 to 62

[0409] The procedure for preparation and evaluation of the photoreceptorin Example 44 was repeated except that the compound No.1 was replacedwith the compound described in Table 9 and the addition amount of theCTM having formula (17) was changed to 7 parts.

[0410] The evaluation results are shown in Table 9. TABLE 9 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 59 4 100Good 105 good Ex. 60 17 100 Good 105 good Ex. 61 25 105 Good 115 goodEx. 62 37 105 Good 110 good

Examples 63 to 66

[0411] The procedure for preparation and evaluation of thephotoreceptors in Examples 59 to 62 was repeated except that the ratioof the compound to the CTM having formula (17) was changed from 1/7 to5/5.

[0412] The evaluation results are shown in Table 10. TABLE 10 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 63 4 100Good 105 good Ex. 64 17 105 Good 110 good Ex. 65 25 110 Good 135 goodEx. 66 37 120 Good 120 good

Examples 67 to 70

[0413] The procedure for preparation and evaluation of the photoreceptorin Example 44 was repeated except that the compound No.1 was replacedwith the compound described in Table 11 and the CTM having formula (17)was replaced with a CTM having the following formula (26).

[0414] The evaluation results are shown in Table 11. TABLE 11 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 67 4 100Good 110 Good Ex. 68 17 100 Good 105 Good Ex. 69 25 105 Good 125 goodEx. 70 37 110 Good 115 good

Examples 71 to 74

[0415] The procedure for preparation and evaluation of the photoreceptorin Example 44 was repeated except that the compound No.1 was replacedwith the compound described in Table 12 and the CTM having formula (17)was replaced with a CTM having the following formula (27).

[0416] The evaluation results are shown in Table 12. TABLE 12 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 71 4 100Good 115 Good Ex. 72 17 105 Good 115 Good Ex. 73 25 110 Good 130 goodEx. 74 37 105 Good 120 good

Examples 75 to 77

[0417] The procedure for preparation and evaluation of the photoreceptorin Example 44 was repeated except that the compound No.1 was replacedwith the compound described in Table 13 and the CTM having formula (17)and the polycarbonate were replaced with 19 parts of a CTM having thefollowing formula (28).

[0418] The evaluation results are shown in Table 13. TABLE 13 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 75 3 95Good 120 Good Ex. 76 8 100 Good 125 Good Ex. 77 17 95 Good 115 Good

Examples 78 and 79

[0419] The procedure for preparation and evaluation of the photoreceptorin Example 44 was repeated except that the compound No.1 was replacedwith the compound described in Table 14 and the CTM having formula (17)and the polycarbonate were replaced with 19 parts of a CTM having thefollowing formula (29).

[0420] The evaluation results are shown in Table 14. TABLE 14 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 78 4 100Good 125 Good Ex. 79 17 100 Good 120 Good

Examples 80 and 81

[0421] The procedure for preparation and evaluation of the photoreceptorin Example 44 was repeated except that the compound No.1 was replacedwith the compound described in Table 15 and the CTM having formula (17)and the polycarbonate were replaced with 19 parts of a CTM having thefollowing formula (30).

[0422] The evaluation results are shown in Table 15. TABLE 15 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 80 17 105Good 135 Good Ex. 81 36 100 Good 120 Good

Examples 82 and 85

[0423] The procedure for preparation and evaluation of the photoreceptorin Example 44 was repeated except that the compound No.1 was replacedwith the compound described in Table 16 and the binder resin(polycarbonate) was replaced with 10 parts of a polyarylate resin (UPOLYMER from Unitika Ltd.

[0424] The evaluation results are shown in Table 16. TABLE 16 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 82 8 110Good 125 Good Ex. 83 17 100 Good 105 Good Ex. 84 24 95 Good 115 Good Ex.85 30 105 Good 125 Good

Examples 86 and 87

[0425] The procedure for preparation and evaluation of the photoreceptorin Example 29 was repeated except that the CGL coating liquid and theCTL coating liquid were changed to the following. CGL coating liquidTitanyl phthalocyanine having 8 parts an X-ray diffraction spectrum asillustrated in FIG. 9 Polyvinyl butyral 5 parts (S-LEC BX-1 from SekisuiChemical Co., Ltd.) 2-butanone 400 parts CTL coating liquid Z-formpolycarbonate resin 10 parts Compound No. 4 or 17 illustrated 1 part inTable 1 or 2 CTM having formula (17) 7 parts Toluene 70 parts

[0426] The evaluation results are shown in Table 17. TABLE 17 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 86 4 115Good 130 Good Ex. 87 17 110 Good 125 Good

Examples 88 and 89

[0427] The procedure for preparation and evaluation of the photoreceptorin Example 86 was repeated except that the CTM in the CTL coating liquidwas replaced with a CTM having formula (19).

[0428] The evaluation results are shown in Table 18. TABLE 18 At thebeginning of At the end of the running test the running test CompoundP_(L) Image P_(L) Image No. (−V) qualities (−V) qualities Ex. 88 4 110Good 125 Good Ex. 89 17 105 Good 130 Good

Comparative Example 4

[0429] The procedure for preparation and evaluation of the photoreceptorin Example 44 was repeated except that the compound No. 1 was replacedwith a stilbene compound having the following formula (31).

[0430] Thus, a photoreceptor of Comparative Example 4 was prepared. Theevaluation results are shown in Table 19.

Comparative Example 5

[0431] The procedure for preparation and evaluation of the photoreceptorin Example 44 except that the compound No. 1 was not included in the CTLcoating liquid and the addition amount of the CTM was changed from 9parts to 10 parts.

[0432] Thus, a photoreceptor of Comparative Example 5 was prepared. Theevaluation results are shown in Table 19.

Comparative Example 6

[0433] The procedure for preparation and evaluation of the photoreceptorin Example 63 except that the compound No. 4 was replaced with atetraphenylmethane compound having the following formula (32).

[0434] Thus, a photoreceptor of Comparative Example 6 was prepared. Theevaluation results are shown in Table 19.

Comparative Example 7

[0435] The procedure for preparation and evaluation of the photoreceptorin Example 44 except that the compound No. 1 was replaced with ahindered amine-based antioxidant having the following formula (33).

[0436] Thus, a photoreceptor of Comparative Example 7 was prepared. Theevaluation results are shown in Table 19. TABLE 19 At the beginning Atthe end of of the running test the running test P_(L) P_(L) (−V) Imagequalities (−V) Image qualities Comp. Ex. 4 320 Low image 550 Very lowimage density density. Images cannot be read. Comp. Ex. 5 100 Good 135Poor resolution Comp. Ex. 6 200 Low image 285 Low image density. Gooddensity. Good resolution. resolution. Comp. Ex. 7 250 Low image 480 Verylow image density. Poor density. Images resolution. cannot be read.

[0437] As can be understood from the data in Tables 7-19, thephotoreceptors of the present invention have low residual potentialafter long repeated use, and can stably produce high quality images fora long period of time.

[0438] In contrast, the comparative photoreceptors have high residualpotential and cause a low image density problem and/or a low resolutionproblem. After the 100,000-sheet running test, the half-tonereproducibility of the images produced by the comparative photoreceptorsdeteriorates, and thereby the images cannot be read. The photoreceptorof Comparative Example 5 has a relatively low residual potential evenafter the running test, but the resolution of the resultant imagesdeteriorates.

[0439] In addition, images were produced using the photoreceptors ofExamples 29, 47, 56, 69, 73, 77, 79, 80, 85, 87 and 89 and ComparativeExample 5 were allowed to settle in a desiccator containing airincluding NOx gasses at a concentration of 50 ppm for four days, tocompare the resolution of the images with that of the initial images ofthe respective photoreceptors.

[0440] The results are shown in Table 20. TABLE 20 Initial Image Imagequalities after qualities the preservation test Ex. 29 Good Good Ex. 47Good Good Ex. 56 Good Good Ex. 69 Good Good Ex. 73 Good Good Ex. 77 GoodGood Ex. 79 Good Good Ex. 80 Good Good Ex. 85 Good Good Ex. 87 Good GoodEx. 89 Good Good Comp. Ex. 5 Good Resolution seriously deteriorated.

[0441] As clearly understood from the data as shown in Table 20, thephotoreceptors including a compound having formula (1) have excellentresistance to NOx gasses (i.e., images having good resolution can beproduced even after the photoreceptors are exposed to NOx). In contrast,the comparative photoreceptor has poor resistance to NOx gasses (i.e.,the images have poor resolution after the photoreceptors are exposed toNOx).

[0442] This document claims priority and contains subject matter relatedto Japanese Patent Application No. 2003-057682, filed on Mar. 4, 2003,incorporated herein by reference.

[0443] Having now fully described the invention, it will be apparent toone of ordinary skill in the art that many changes and modifications canbe made thereto without departing from the spirit and scope of theinvention as set forth therein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:
 1. A photoreceptor which includes an electroconductive substrate, and a photosensitive layer located overlying the substrate, wherein the photosensitive layer comprises a diamine compound having the following formula (1):

wherein R1 and R2 independently represent a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aromatic hydrocarbon group, wherein at least one of R1 and R2 is a substituted or unsubstituted aromatic hydrocarbon group and R1 and R2 can optionally share bond connectivity to form a substituted or unsubstituted ring including a nitrogen atom; and Ar represents a substituted or unsubstituted aromatic hydrocarbon group.
 2. The photoreceptor according to claim 1, wherein the photosensitive layer further comprises a charge transport material.
 3. The photoreceptor according to claim 2, wherein the charge transport material is a compound selected from the group consisting of stilbene compounds having the following formula:

wherein n′ is 0 or 1; R1 represents a hydrogen atom, an alkyl group or a substituted or unsubstituted phenyl group; Ar1 represents a substituted or unsubstituted aromatic hydrocarbon group; R5 represents an alkyl group having from 1 to 4 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group, wherein Ar1 and R5 optionally share bond connectivity to form a ring; and A represents a 9-anthryl group, a substituted or unsubstituted carbazolyl group or a group having one of the following formulae:

wherein R² represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom or a group having a formula of ═N (R³)(R⁴), wherein R³ and R⁴ independently represent a substituted or unsubstituted aromatic hydrocarbon group, and R³ and R⁴ optionally share bond connectivity to form a ring; and m is an integer of from 1 to 3, wherein when m is not less than 2, each of R² is the same or different from the others, and wherein A and R1 optionally share bond connectivity to form a ring when n′ is 0; aminobiphenyl compounds having the following formula:

wherein R11, R13 and R14 independently represent a hydrogen atom, an amino group, an alkoxy group, a thioalkoxy group, an aryloxy group, a methylenedioxy group, a substituted or unsubstituted alkyl group, a halogen atom or a substituted or unsubstituted aromatic hydrocarbon group; R12 represents a hydrogen atom, an alkoxy group, a substituted or unsubstituted alkyl group or a halogen atom; and j, k, p and w are independently an integer of from 1 to 4, wherein each of R11, R12, R13 and R14 may be the same or different from the others when j, k, p and w are an integer of from 2 to 4; charge transport polymers having the following formula:

wherein R7 and R8 independently represent a substituted or unsubstituted aromatic hydrocarbon group; Ar2, Ar3 and Ar4 independently represent an arylene group; c is a number of from 0.1 to 1.0 and d is a number of from 0 to 0.9; n is an integer of from 5 to 5000; and X represents a divalent aliphatic group, a divalent alicyclic group or a divalent group having the following formula):

wherein R101 and R102 independently represent a substituted or unsubstituted alkyl group, a substituted or unsubstituted aromatic hydrocarbon group, or a halogen atom; s and t represent 0 or an integer of from 1 to 4; v is 0 or 1; and Y represents a linear alkylene group, a branched alkylene group, a cyclic alkylene group, —O—, —S—, —SO—, —SO₂—, —CO—, —CO—O-Z-O—CO— (Z represents a divalent aliphatic group), or a group having the following formula:

wherein a is an integer of from 1 to 20; b is an integer of from 1 to 2000; and R103 and R104 independently represent a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aromatic hydrocarbon group, wherein R101, R102, R103 and R104 may be the same or different from the others; and charge transport polymers having the following formula:

wherein Ar11, Ar12, Ar13, Ar14 and Ar15 independently represent a substituted or unsubstituted aromatic hydrocarbon group; Z represents an aromatic group or a group —Ar16-Za-Ar16, wherein Ar16 represents a substituted or unsubstituted aromatic hydrocarbon group, Za represents O, S or an alkylene group; R and R′ independently represent a linear or branched alkylene group; h is 0 or 1; and X, c, d and n are defined above.
 4. A photoreceptor comprising: an electroconductive substrate; a photosensitive layer located overlying the electroconductive substrate; and optionally a protective layer located overlying the photosensitive layer, wherein an outermost layer of the photoreceptor comprises a filler, an organic compound having an acid value of from 10 to 700 mgKOH/g and a diamine compound having the following formula (1):

wherein R1 and R2 independently represent a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aromatic hydrocarbon group, wherein at least one of R1 and R2 is a substituted or unsubstituted aromatic hydrocarbon group and R1 and R2 can optionally share bond connectivity to form a substituted or unsubstituted ring including a nitrogen atom; and Ar represents a substituted or unsubstituted aromatic hydrocarbon group.
 5. The photoreceptor according to claim 4, wherein the photosensitive layer is the outermost layer.
 6. The photoreceptor according to claim 4, including the protective layer, wherein the protective layer is the outermost layer.
 7. The photoreceptor according to claim 4, wherein the organic compound having an acid value of from 10 to 700 mgKOH/g is a polycarboxylic acid.
 8. The photoreceptor according to claim 7, wherein the polycarboxylic acid is a material selected from the group consisting of polyester resins, polyester copolymers, acrylic resins, and acrylic copolymers, which have a plurality of carboxyl groups.
 9. The photoreceptor according to claim 4, wherein the outermost layer further comprises a fatty acid.
 10. The photoreceptor according to claim 4, wherein the filler an inorganic pigment.
 11. The photoreceptor according to claim 10, wherein the inorganic pigment comprises a metal oxide.
 12. The photoreceptor according to claim 10, wherein the inorganic pigment has a pH not less than
 5. 13. The photoreceptor according to claim 10, wherein the inorganic pigment has a dielectric constant not less than
 5. 14. The photoreceptor according to claim 4, wherein the filler has an average primary particle diameter of from 0.01 to 0.5 μm.
 15. The photoreceptor according to claim 4, wherein the outermost layer comprises a charge transport material.
 16. The photoreceptor according to claim 15, wherein the charge transport material is a charge transport polymer material.
 17. The photoreceptor according to claim 4, wherein the outermost layer further comprises a binder resin selected from the group consisting of polycarbonate resins and polyarylate resins.
 18. The photoreceptor according to claim 4, wherein the outermost layer further comprises an antioxidant selected from the group consisting of hydroquinone compounds and hindered amine compounds.
 19. An image forming method comprising: charging the photoreceptor according to claim 1; irradiating the charged photoreceptor with imagewise light to form an electrostatic latent image on the photoreceptor; developing the electrostatic latent image with a developer including a toner to form a toner image on the photoreceptor; and transferring the toner image on a receiving material.
 20. An image forming method comprising: charging the photoreceptor according to claim 4; irradiating the charged photoreceptor with imagewise light to form an electrostatic latent image on the photoreceptor; developing the electrostatic latent image with a developer including a toner to form a toner image on the photoreceptor; and transferring the toner image on a receiving material.
 21. An image forming apparatus comprising: the photoreceptor according to claim 1; a charger configured to charge the photoreceptor; a light irradiator configured to irradiate the charged photoreceptor with imagewise light to form an electrostatic latent image on the photoreceptor; an image developer configured to develop the electrostatic latent image with a developer to form a toner image on the photoreceptor; and a transferring device configured to transfer the toner image onto a receiving material.
 22. The image forming apparatus according to claim 21, wherein the light irradiator comprises at least one of a laser diode and a light emitting diode.
 23. An image forming apparatus comprising: the photoreceptor according to claim 4; a charger configured to charge the photoreceptor; a light irradiator configured to irradiate the charged photoreceptor with imagewise light to form an electrostatic latent image on the photoreceptor; an image developer configured to develop the electrostatic latent image with a developer to form a toner image on the photoreceptor; and a transferring device configured to transfer the toner image onto a receiving material.
 24. The image forming apparatus according to claim 23, wherein the light irradiator comprises at least one of a laser diode and a light emitting diode.
 25. A process cartridge comprising: the photoreceptor according to claim 1; and at least one a charger configured to charge the photoreceptor; a light irradiator configured to irradiate the charged photoreceptor with imagewise light to form an electrostatic latent image on the photoreceptor; an image developer configured to develop the electrostatic latent image with a developer to form a toner image on the photoreceptor, a transfer device configured to transfer the toner image onto a receiving material, a cleaner configured to clean a surface of the photoreceptor, and a discharger configured to discharge the charges remaining on the photoreceptor after the toner image is transferred.
 26. A process cartridge comprising: the photoreceptor according to claim 4; and at least one a charger configured to charge the photoreceptor; a light irradiator configured to irradiate the charged photoreceptor with imagewise light to form an electrostatic latent image on the photoreceptor; an image developer configured to develop the electrostatic latent image with a developer to form a toner image on the photoreceptor, a transfer device configured to transfer the toner image onto a receiving material, a cleaner configured to clean a surface of the photoreceptor, and a discharger configured to discharge the charges remaining on the photoreceptor after the toner image is transferred.
 27. A method for manufacturing the photoreceptor according to claim 4, comprising: preparing an outermost layer coating liquid comprising a solvent, the filler, the organic compound having an acid value of from 10 to 700 mgKOH/g, a diamine compound having formula (1), and an antioxidant; and coating the outermost layer coating liquid followed by drying to form the outermost layer.
 28. The method according to claim 27, wherein the antioxidant is a compound selected from the group consisting of hydroquinone compounds and hindered amine compounds. 